how do i join a tourny that give prizes

If you keep yourself updated on the tournament section, you will see post regarding Tournaments, Events, or anything related to that. ESL is starting up and WOGL is also doing some things within the community. Just watch the forums and watch for annoucements within Z8Games because they usually do update the community with competitive related subjects.

They make Annoucements here also: Click Here
That is the tournament part of the website. It is seperate from the forums but its a good way to keep yourself updated competitively.