Sign in to your Epic Games account, then click the button to claim one $10 Epic Coupon (to use on eligible games of $14.99 or above or local currency equivalent). The $10 Epic Coupon will be applied automatically at checkout. Note: If you make your first purchase or grab your first free game during the promotion before clicking on the button you will automatically receive your first $10 Epic Coupon. Coupons expire on May 1, 2020 2:59am EST.
Use the $10 Epic Coupon to buy an eligible game of $14.99 or more on the store (during the promotional period) and you’ll receive another $10 Epic Coupon. Note: Coupons expire on May 1, 2020 2:59am EST.
sounds a bit confusing but basically $10 off any purchase (I believe this can only be an individual game as the store doesn't seem to have a cart feature)
the store also has their summer sale going on, so with the further $10 off you could get games like Jedi Fallen Order or Red Dead Redemption 2 a fair bit cheaper than on steam, or some games around the $15 mark very cheap: Assassins Creed Origins, South Park the Fractured but Whole, and The Crew 2 are [US]$7.48, Heavy rain is [US]$7.99