There are lots of websites known as social networking sites, and many are being used more and more as a source for news stories.
These sites are popular with adults, but people using them need to be very careful to keep themselves safe by not giving away personal details.
Here's a rundown of some of the most commonly-used.
Facebook is one of the most popular and well-known social networking sites.
The idea behind it is to help people keep in touch with their friends and let them know what they're doing or thinking.
People create profile pages where they can include as much or as little information about their lives as they want to.
But the founders say they'll delete the accounts of anyone under the age of 13 and ask for permission from parents of anyone aged 13-18.
They can share photos and videos online or promote links to other content that they think their friends might like.
But as with any of these sites, it's important to be really careful about what personal information you share online.
Twitter is slightly different to most social networking sites as it's more of a micro-blogging site.
Instead of having a profile page where you tell people all about your likes and dislikes, Twitter asks everyone just one question: "What are you doing?" Their answers - known as Tweets - are limited to 140 characters - letters, numbers or spaces.
Loads of celebs use Twitter, and it's been the source of many news story, for example Keisha leaving the Sugababes and Miley hitting back at her cyber bullies.
But there are lots of people pretending to be celebs too - so be careful not to believe everything you read on the site.
You have to be at least 13 years old to create an account on MySpace.
But you can access loads of music and video clips on the site without having your own profile page.
Anyone with an account can link up with their friends online, share music, photos and video clips and even create playlists of their favourite content.
Another social networking site that lets people keep in touch with their friends online.
You have to be 13 or older to use the site and as well as uploading personal information, you can share your thoughts, photos and videos too.
If you want to watch or share video clips online, this is the site most people use to do it.
You can watch any of the clips online, as long as they're not rated 18.
But you have to create an account if you want to put your own videos online and you can't do that unless you're over 13 years old.