If you ordered $90 of Stampin' Up! product in August, you earned a $9 voucher. Not only that, for every $90 of product you ordered in August you earned a $9 voucher!
You should have received an email from Stampin' Up! at the end of August telling you how many vouchers you have and giving you your voucher codes.
Remember to REDEEM your rewards in September, or they will disappear!
Just place an order this month by adding what you want to your order, then the order form will show you a link saying 'manage coupon codes'. Just click on that, enter your codes, and watch the cost of your order be reduced by $9 for every voucher.
If you decide you didn't want to use a coupon code, you can remove it.