Most merchants use coupon codes that are entered in during the checkout process.
Simply click on the coupon link and you will be taken to the merchant's site. Once at the merchants site you will notice a small pop-up window toward the top of the screen. In this window you will find the coupon code and expiration date listed for the deal you clicked. Also, in this window you will notice a pull down box which you can use to select other deals the merchant is currently running. To redeem a deal without a coupon code simply click the coupon link which will take you to the merchant's page where the offer can usually be found.