These coupons are being attached to the bottom of the receipt for every in-store purchase transaction. I believe the coupons will be offered the whole month of July, and ready to be used in August.
They only used to offer 25% off with these coupons.
You can also get the coupon with the current offer where 20% is taken off the whole transaction if you purchase an item with a "Markdown" or "Special Price" label. (see here for details, valid until 16th)