If you plan on entering a tournament for a game, you have to pay a venue fee. If you just want to watch, you don't have to pay anything. After you pay the venue fee, you pay the fee for the game you want to enter. Some might be more than others... for example, MK is $5 I think while Injustice is $10. As far as signing up, you just go up to the tournament organizer, give them the required money, and tell them the name you'll be entering under. There's a cutoff for the signups and once that cutoff occurs, the brackets are made and then the tournament starts.