Tournaments
The Tournaments screen lists the tournaments you are entered in, and lets you manage them by putting or removing money from your Tournament funds.

You may also use this screen to Withdraw from a tournament, if you withdraw you can not enter the tournament again until it resets on the coming Sunday during maintenance.

To enter a tournament you have to goto an Arena these commonly have a Tourney Host inside who will let you enter.

You will then be able to fight other players in the tournament, some tournaments have different rules and requirements and every Sunday tournament winners are announced.