First you will want to sign into your account (or create a free account).
Once you are logged in, go to the class that you want and add it to your cart.
After the class is added to your cart, you can select GO TO CHECKOUT
This page shows that you will not have a shipping fee. Just click on CONTINUE CHECKOUT.
On the second page of the checkout process, you will see a box that says Redemption Code. That is where you will enter the promo code for the class you are taking. Once you have entered the code, choose your method of payment, and select CONTINUE CHECKOUT.
If you entered a valid code, you will see a Congratulations notification at the top, and you will notice that the discount has been take off of your cart total. Click on CONFIRM THE ORDER to pay.