To apply a coupon using a code, navigate to the menu screen.
Create the order and click on the Options button.
In the options screen click on coupon.
Type the coupon code into the text box.
Click ok and the coupon will be applied to the order. If it is not a valid code, you will receive an error.
Of course, these coupons may also have other restrictions, so be sure to order the proper required items before applying the coupon code.