Just enter a qualifying discount code during your online check-out. No need to bring a coupon with you. However, remember for association or corporate discounts you will need to present a qualifying ID, at time of return.
How do printed coupons work?
Coupon discounts will not be reflected in your reservation quote, they will be applied at the location. Simply print the coupon and take it with you on your trip, and presented it to the cashier upon return.