Shop for eligible items. (See below for exclusions).
Pay for your item by 10:00 PM Pacific Time on August 28, 2018
Enter the Coupon code in the redemption code field: PREGAME15
It's a one time use code, and the exclusions were things like handling, shipping and tax. There is a $25 min purchase and a $100 max value, so I guess you can only spend $667 to receive the full discount.