Read the rules. Last time I checked, you need to critique at least two other members' work, and post twenty times before you can post your own work for review.
Thanks guys! One more question : The weekly writing contests, do they have any requirements and where is the basic rules of them? I looked, I really did, but can't find them. I'm blind >_<
The contests all begin with a post outlining the rules and the theme for the current competition. For any questions, send a private message to the staff member in charge of the contest (the one who posted the starting post of the thread). As for submitting for critique, there is a panel on the home page, labeled Important Information. It is not mislabeled.