Use Coupon Code at GoDaddy is easily:
Add the products you want to but at GoDaddy.com
Go to the shopping cart page, at the right side of this page, below the Subtotal, GoDaddy ask you Have a promotional code?
Click Add link, and you will be prompted to enter the coupon code.
When you enter the coupon code in the box, click Apply link. If the promo code you enter is valid, your subtotal will reduce amount of the discount. If not, the subtotal remain the same.
After redeem the coupon, you can continue to checkout.
There is a picture figured out how to use GoDaddy promo code at shopping cart:
PS: Yon can find the latest GoDaddy Promo Code at Dacoz.com.