What is a fraternity?

What is a fraternity and sorioty? Not sure if Im spelling that right? I know its some sort of college group thing in America, but what is the purpose of them and how does it all work? Do you have to live in the student house? I find American stuff facinating, we dont have anything like that in the UK although kids are now starting to have prom, but its not as popular as it is in America. Ive heard college football (American Football) is really popular in USA like premier league soccer is here. Is that true?