You can use your discount codes to pay or partially pay for your order. It is very easy to enter a discount, or promo code, on the site:
1. Put all the products in your basket
2. Go to the basket screen and put in the discount code:
3. Click "Apply." The discount will automatically be applied, and the new basket total will reflect the discount.
The product totals will also adjust to show the discounted price.
The total discount value will also show in the cart/basket.