they put in a form and they get the head of the country to sign it and then they prepare!
Members of the IOC (Internation Olympic Committee) choose the next venue for the Olympic games, which must be a city rather than a country. So, for example, the next Olympics,, in 2012, will be hosted by London, rather than England.
any city which wishes to hose the games put their bid to the IOC. Only one city from each country can bid, and even putting forward a bid takes a huge amount of work and is very expensive.