The discount code needs to be entered into the discount code box at checkout. You are only able to use one discount code on any given order, meaning if you have multiple codes, you would want to use whichever is best.

Discount codes do not work on a subscription order, the code will not be valid as subscriptions are ineligible for additional discounts.

Once you have your discount coupon, be sure you enter it into the box on the checkout page (pictured here).

insert the code in the discount codes box during checkout