On every displayed coupon, there is a field called Coupon Code

Sometimes you don’t need any code to shop with the coupon. In this case, simply click the coupon link or the Shop Now button and the coupon discount/offer will automatically be applied to your order during the store’s checkout process.

If a coupon code is required, click on the coupon code and it will automatically get copied. You will then be taken to the store where you can add products to your shopping cart, and then look for the Promotion Code or Coupon Code field during the checkout process. Paste the coupon code here. Click the Update or Submit button if there is one. Proceed to checkout.

Note: If you click the Shop Now button on the coupon which requires a coupon code, make sure you first copy the code by highlighting it, right-clicking, and selecting Copy. Then proceed as given above.