1. Click the Coupons at Checkout icon on the toolbar and then click "Submit a Code" on the lower left (as seen pictured below).
2. In the dialog that pops up, enter the website (domain name only - eg. amazon.com), the coupon code, the discount description, and an expiration date if applicable.
Note: For users of Coupons at Checkout versions prior to 2.0, similar functionality can be accessed by going to couponfollow.com and clicking on "+ Code" in the menu bar near the top of the page.