These are some of the main parts of the EU.
The European Parliament
This makes laws and helps to decide how much money the EU should spend. It also checks that all the other parts of the EU are working fairly.
Members of the European Parliament (MEPs) are elected every five years. Anyone over 18 from a member country may vote.
Council of the European Union
This is where the EU's big decisions are normally made.
It's like a school council, but instead of people from each year there are people from each country.
Who turns up depends on what the council is talking about. If they are talking about farms then the 25 ministers for farming would go along, one from the government of each country.
The European Commission
The European Commission does the day-to-day work of running the EU.
It does things like making sure that
that the laws the European Parliament passes are used properly.
Every six months a different country gets the presidency of the EU. With 25 members the UK's turn only comes round every 12 and a half years.