The shopper can enter the coupon codes in one of two places. 

First, as long as you have a coupon in your system, the customer will see a notice and a place to enter the coupon on the shopping cart.  After they enter their coupon and update their cart, they will see the effects of the coupon.  If their order does not meet the criteria of the coupon they will see an message at the top of the cart.

Second, at the payment page of the check out process, there will be a place for entering the coupon id.  When they get to the confirmation page, they will see the effect of the coupon.   However, since the coupon was entered after the shipping method has been selected by the customer, the system does not know if the customer wants the free shipping or some other method such as “next day.”  Therefore, the customer will be promoted to return to the shipping selection page to select the method they want. 

After the order is complete, a confirmation email will be sent to the shopper and to you, the merchant.  The message will indicate the coupon selected and the effect.  When you go to “Retrieve Orders” you will also see the coupon selected.