Facebook is a vast, sprawling network and you can make whatever you want of it. You sign up by putting some details, and preferably a photo of yourself, on the Facebook website. Then you’re ready to start posting a few updates.
These updates are statements about what you’re up to, links to interesting stuff you’ve seen elsewhere on the web – it’s up to you. As word gets around that you’re online, you’ll find old friends start to get in touch. They may have heard about you being on Facebook or they may have found you after doing a search.
Facebook itself will send notes on people you might know, based on the fact that you went to the same school or college or shared an employer (you only have to put up as much of this sort of information as you want).