On the eve of the anniversary of the terrible events of 11 September, Newsround's presenter Lizo Mzimba answered your questions in a live webchat from New York.
He was joined by Emily. She lives close to the World Trade Center and saw the attacks.
During the past year she and her school friends have been coming to terms with what happened.
If you missed the live version, you can still catch up on the chat by clicking the link below:
Watch video webchat
Obviously there have been a lot of people coming to pay their respects but have there been people from abroad too?
Lizo: Oh yes, New York is full of people from all over the world and some of the memorials that are still around - there's whole railings where people have put flowers and messages. The really touching thing is that so many of them are from people all over the country, all over the world, and they say where they're from and what they feel about what's happened and I think it's something that really has touched people in New York. But it's not just people in this city or across America that feel terrible about what happened, it's people from all over the world that have been really sharing in their grief for the past 12 months.
Annie, 14, London
What was the first thing you thought when you saw the attacks?
Emily: Well I went into a complete blur basically and I just thought of my dad on an aeroplane on his way somewhere and I just thought of my mum being right there where the planes had hit and I couldn't think of anything around me, I just was completely phased out.
Kaleigh, 14, Connecticut, USA
Where were you when the attacks happened?
Emily: I was in my social science class in school.
Hannah, 12, Milton Keynes
How did you feel when you saw the attacks?
Emily: I felt like who could do something of such a horror to our city and such a wonderful country? I couldn't compute why would someone want to do that.
Don, 12, Gravesend
Seeing the first plane crash what was your immediate reaction?
Emily: I was worried that something was going to happen - bigger and much worse than that and my first reaction was my mum - where was she? And I was just worried for her.
Vicky, 12, Wiltshire
What does it feel like being in America, in the country, where this terrible thing has happened?
Emily: That's a question I don't know really how to answer, I was so scared that something else was going to happen, I don't really know how to answer that question.
Was it almost like the nation was in mourning?
Emily: Yeah I was scared for everything going on and felt something much worse was going to happen around us.
Natasha, 10, Bexhill
What does Ground Zero look like now?
Lizo: Yes there's still an awful lot of activity going on there - bits of construction, cranes, diggers. I mean compared to, of course, what it was a year ago, when we were first out here, the area is a lot, lot smaller and the operation of what's going on there has been scaled down because an awful lot of work has been done there over the last 12 months. But there are people still working away there. And the really touching thing is that as you're walking around Ground Zero, down there, there are still people coming to see the place and people just looking on with sadness. We bumped into one person there who worked in the World Trade Centre and it's the first time he'd been back there since it all happened last year and we spoke to him very briefly. And people just come to see where it happened and I think many people still do find it hard to comprehend something of this scale of what did happen here 12 months ago.
Thomas, 10, Chegrave
What will we put in the space where the towers fell?
Lizo: Well there's still lots of debate going on, I mean everybody, I think, agreed that there is going to be some kind of memorial there but as to what that memorial exactly will be - I think they're still taking their time to make sure they get it precisely right so that everybody is really happy with what does happen there. There will be something to remember the victims of the twin towers and they're still really talking about exactly what form that is going to take but whatever it is they know it will be something very special.
Hadra, 13, Queens, New York city
Lizo, how does it feel being there, do you feel like the atmosphere is different because of 9/11?
Lizo: I think, certainly when I first came out a year ago for the attacks the atmosphere was incredibly, incredibly different, it really was a city first in shock and then really bonded together in patriotism - there was American flags flying everywhere, people were saying this terrible thing has happened but they can't really break the spirit of the people of New York. A year on and that spirit is still very much there - people are still very warm, very affectionate, obviously they're very saddened by what happened. They are moving forward though but there is a real atmosphere that New York is an incredibly strong city, the people here - the bonds between people here and the friendships - and it's something that can never be destroyed by no matter how terrible an event.
Lisa, 12, Crewe
Does it affect Americans each day? How does it feel waking up and seeing those twin towers gone?
Emily: There's an empty space there, the city's not the same without it. Every morning it's a constant remembrance of what happened and such a terrible tragedy.
Do you think people show their emotions more in New York now because of what happened?
Emily: I think - yes and no.
Matthew, 14 Gateshead
Do you think they're coping?
Lizo: They are, people are strong aren't they. I mean there's a lot of sadness about but all the people we've spoken to - obviously it's something that they still talk about every day, it's something that happened to their city but, as I said before, they are moving on and they say there's nothing going to break the spirit of friendship and the bonds that New Yorkers do have.
Fahid, 12, South West London
Do you think it's safe to go on an aeroplane since 9/11?
Emily: Yes everyday when I see a plane in the air I just look up and I think where is it headed now? I don't think seeing a plane you'll ever think of something different for most of the time.
Lizo: There have been lots of improved security measures both here and across the world after what happened and the airlines have talked about very much how they're trying to make sure that something like this could never happen again - making cockpit doors stronger, making security much stricter for people getting on to aircraft.
Amber, 13, London
Does President Bush actually have proof that Bin Laden actually did it?
Lizo: Well the American government very early on said that this was the person with his network of terrorists called al-Qaeda who they believed was responsible. Obviously the way that governments work they don't show everything to everybody saying look here's the proof that somebody did this but the elected president of American, George Bush, has says that he believes very strongly from the evidence that he has and evidence from around the world that Osama bin Laden was the person responsible and he's talked about the actions he wants to take against Osama bin Laden.
Nicholas, 13, Doughton
Why haven't we found him yet?
Lizo: Well they've been looking very hard and of course there was the war against terrorism in the country of Afghanistan where they went to look for him. It's a big country and he's very well protected. So it's difficult to say why they haven't found him. I think they're trying very hard. The government here have said the war against terrorism's more than the war against just one man, it's not just a war on Osama bin Laden, it's a way against everything he stands for and they've said they're determined to smash his al-Qaeda terrorist network and whether they get him or not isn't the whole story, if they can stop terrorism happening across the world then that's the most important thing. That's the view of the American government I believe.
Jon, 11, Yeovil
Does it matter if we never find him?
Lizo: Well again, as I said, the American government say that the war of terrorism is more than a war on one man so even if they never find him but they have stopped terrorist attacks like this happening and made people feel safer, both in America and across the world, the American government say that is the most important thing.
Siobhan, 13, Newcastle-upon-Tyne
If terrorists strike again do you think America will be ready for them?
Lizo: I think that America obviously in the last 12 months has made all sorts of moves towards improving its security, improving its intelligence, the way that terrorists work and trying to stop terrorists attack before they happen. How ready is a country ever for a terrorist attack? I think the American government said the main thing that they want to do is stop the attacks happening in the first place, rather than waiting for an attack to happen and then sort of reacting to that afterwards. So I think the only real true answer to that is to see what does happen after an attack but the American government say that even if attacks do happen and various voices think attacks may well happen and they have ways of coping with that.
Sadaf, 15, Rochdale
How has the relationship changed between Americans and Muslims after the attacks?
Lizo: Well we've spoken over the last year to Muslim children living in America and I think now, 12 months on, the relationship is very strong. Initially there were lots of incidents and stories of Muslim children being bullied, badly treated because of what had happened. But I think as time has progressed people have actually learnt that it's not about discriminating against somebody because of their religion, it's the Americans trying to stop terrorists attacks happening again.
Jo, 11, Bath
Do you think about Afghanistan that much? You have suffered a terrible lot but so have they.
Emily: Yes I do, I think that what has happened to them, I don't just think of myself when I look at the twin towers everyday or I see it on the news. I think about what they're going through and that it's not just their fault, it's actually Osama bin Laden's, not the people around there - I don't think they should be affected by it as much as we're affecting them.
Do you think America has become a stronger nation after these attacks?
Emily: Most definitely, I totally think that everyone has come together as one and the city has just gotten a lot better.
Lizo: Coming in as an outsider that's something I've definitely noticed that every where we go there are American flags, there's a real sense of comradeship, people have really re-emphasised how strong the American country is. And I think after the attacks - that spirit was there before but it's certainly much more obvious to people coming here.
Kriti, 12, Essex
Lizo approximately how many people were killed when the World Trade Centre collapsed?
Lizo: Approximately just over 2,800 people were killed here when they collapsed at the World Trade Centre situated just behind me here.
Mandy, 12, Edinburgh
How big is that area?
Lizo: The area we're looking at here, it's probably about 200 metres by 300 metres and there's still lots of activity going on there - lots of construction work, all the clearing away has really happened it's just putting in lots of other things that need to be sorted out there before building can start in that area again. And as I said before the really touching thing around there is that there's an incredible amount of memorial material - there's notes from people around the area of Ground Zero, there's flags from countries all over the world, and people scribbling just messages of appreciation - people of all ages, people from all countries across the world.
Tim, 12, Kingskerswell
How have the hero firemen, the police officers and people who lost their lives been commended - have they built statues?
Lizo: Well there are various things going on here in the way of memorials. I think Emily would agree that those kind of people are real heroes to the American people here. And I think that all the people - victims and heroes and everybody who suffered because of September 11th will find themselves commemorated in an appropriate way.
Emily, how much time did you get off school after September 11th?
Emily: I got the next day off and then just personally I took the next day off because I wanted to make sure my dog got out of my apartment ok but the whole school got out one day.
And is tomorrow going to be a national holiday?
Lizo: No it's not, I mean a few schools are closing, a very few, but I think the people want businesses and schools and things to open here as normal, almost as if to say that life goes on, we will commemorate what happened and remember those who did die but life in America will go on as normal - shops will open, schools will open, businesses will open, although they'll be things like a minute's silence at 1346, the time that the first aircraft struck the tower. But I think those people want to give the feeling to the world that things are moving back to normal.
How long did it take New York to get back to normal?
Emily: Since January things started getting ticked off. I moved back in March, 1st March, everything started getting back to normal around January.
What did your school do when you heard about the twin towers?
Emily: Well my school talked about it a lot for the first week. They went around and made sure everyone was ok. I went to special counselling where they made sure everything was ok with me. A few kids I think were a little traumatised by it, I know people around the neighbourhood of kids have post traumatic syndrome now from seeing everything. But the school handled it in a sensitive way in the most part.
What do you think about the people who were there writing songs and books and poems etc. about September 11th?
Emily: I think they're very moving. I like how people read poems and sayings and things, I think I actually enjoy reading them and I have books on them and every once in a while I'll go through them and see them, I like it.
Lizo: I think it's whatever helps them or other people cope with and get over what happened, if people want to do that by writing songs or poetry then they have to do what means the most to them to be able to move on from what was a really terrible, terrible tragic event here.
Stevie, 13, Gloucester
Is there any possibility of another terrorist attack on the one year anniversary tomorrow?
Lizo: What I can tell you is that here in New York around this whole area security is incredibly tight. To give you an example, just to come up here from where I'm doing this broadcast I've had to have two separate security passes just to be able to get up here. So who can say what is being planned but America's worked very hard to do their absolute best to stop any further attacks happening. Security is tight, people are so vigilant - ready to report anything out of the usual. No one can look into the future but as I said I've never seen security quite as tight as it has been up here.
Do you think Britons are doing enough to observe September 11th and remember the people who died?
Lizo: I think so. It's a year on, people are remembering what happened in their own way - the services they can take part in, there's memorials going on - and I think that people here in New York really do appreciate what is happening across the world and they're very touched by the fact that even a year on people across the world have been very moved about what has happened.
Emily: I think that there shouldn't be a day off from school because some kids, even though they shouldn't, will just think of it as a holiday and do things and I don't think they would always remember what happened and I think just a moment of silence is a good way and I'm hoping tomorrow everyone will just when it's quiet at 8.46 at my school I hope the whole school's silent and that it will feel like everyone's come together as one.
What's going to happen tomorrow to remember the attacks?
Lizo: There's going to be various ceremonies going on here. There's a minute's silence at 1346 which is the exact time that the first plane hit the tower. Later on the relatives of victims are going to be laying roses down at Ground Zero. President George Bush will also be coming down to visit Ground Zero. There's going to be candlelit services in the evening. In the UK there's a service at St. Paul's Cathedral - a memorial service. And just across the world whether in big occasions or very privately by themselves people are going to be looking back and remembering what happened.