How to enter MLG season's?

I am just kind of finding out about MLG and I realized they have like season's and the best teams get to go to a tournament or something (Someone correct me if I have all this wrong) and I just want to know how I can enter the season with my team and compete. Just leave a link with more info about this or just tell me below. Also how can you sign up for the pro circuits? The game I want to do all this with is Black Ops for 360