How do I begin a tournament, I've never played one?

First: subscribe
Second: look for a suitable open tournament and click"enter tornament"

What differences are there between a tournament and a normal game?
Is it only that if you win a tournament you gain more points and if you lose one you lose more points, are there any more differences?

There's no difference in a "normal" rated game and a tournament game related to your "points." However, in a tournament game you have the opportunity to win a tournament as well as games. Some tournaments may have you play only one person (two games) at a time. Other tournaments may have you play many players at the same time giving you an abundance of games to play simultaneously.

in addition to what kwgoodwin said, by playing in tournaments you somehow get the feel of where you stand as a player and the ratings make more sense in the long run

Originally posted by AlenaGrig
What differences are there between a tournament and a normal game?
Is it only that if you win a tournament you gain more points and if you lose one you lose more points, are there any more differences?