How do I use promo codes?

On the final checkout screen you will see the following box to enter in your promo code:

When redeeming a promo code, a minimum purchase is required after all coupons, discounts, substitutions, and out of stock items are applied to the order. No cash back. Promo code must be presented at the time of purchase. Limit 1 use per Rewards! account. Limit 1 promo code per transaction.