The Deals tab has coupons and current deals.

You get Reward Points when you do anything on the site - upload art, enter a contest, upload a freebie, upload a product, buy something, post a review of something you bought. When you have enough points, you can turn them into gift certificates. 500 points gets you a $5 certificate. Each 500 points gets you another $5. If you had 1000 points, you could get a $10 certificate. But it expires, so it's best to get the certificate when you plan to use it. Also, new points are held for 24 hours as "pending." You can press your username top right and select Rewards in the flyout to see more about that.

It works well once you get used to it.