Start by signing up for an account, which requires little more than your name and e-mail address. Wait for your confirmation e-mail to arrive, then click the link to activate your account. Now you're all set to start shopping.

Let's say you're in the market for some flowers for Mother's Day. Instead of going directly to, say, 1-800-Flowers.com, you'd head to FatWallet's , search for that store, then click through to it using FatWallet's affiliate link. From there you just browse and buy as usual.

Flash forward several months. (Yes, it takes that long--this is not unlike waiting on a rebate check. And I suppose that's the "catch.") After FatWallet receives confirmation from the merchant that you've paid for your product (and haven't returned it), you'll see a Cash Back credit in your account.

The amount varies from one store to another--it might be three percent of your total purchase price, or eight percent, or even 15. When you're ready to turn that credit into actual money, you can request a check or a direct transfer to your PayPal account. I recommend reading so there are no surprises along the way.

Although a few percentage points might not seem like much, it can definitely add up--especially on big purchases. If you drop $800 on a new TV, and the merchant is offering 10 percent, that's $80 back in your pocket. And if you place a monthly order with, say, the Vitamin Shoppe, you'll get seven percent back every single time.