Somebody explain facebook to me.

I have a facebook account. People I know send me invites to be their friends. Ok, so I accept them as friends. Then I get six zillion stupid games and quizzes and other bullshit that would normally show up in a spam filter if this was email. Then, if they want, they can send me a message. Can't they just send me a real email? What the fuck it this for? It really pisses me off. What do people do with it? I don't want to take a movie quiz, or play virtual tag or some other bullshit. Am I missing something?