You can enter the promo (or coupon) code on the Checkout page. Just make sure to click "Apply" once you've entered it.
Please note, there's a limit of one promo code per order and exclusions may apply (see here for the current list). Also, some of our promo codes do require you to be logged into your Food52 account. If you don’t yet have a Food52 account, you can sign up for one by visiting Food52.com and clicking the blue "Sign Up" button in the top right-hand corner of the page.