To set the coupon's redemption limit, go to:

Site/Courses > Coupons > Create Coupon

The 'Redemption Limit' is the maximum number of times a coupon can be used. If you wish for it to be used for an unlimited number of times, simply leave it blank. But if you want to apply a maximum number of uses, you can enter the number into the redemption limit field. This way, it gives you complete control over the number of coupons that are being used by the system.