You can create coupon to offer your customers discounts. To do this, activate coupons on the "Manage Store Setting" page.
From the main Web Store page in the Builder, click on Settings.
On the "Manage Store Settings" page, scroll down to "Coupons" under "Premium features."
Click Add Coupon and enter your Code, the Discount amount (or percentage off) and the Duration (how long the coupon code will be valid).
NOTE: Coupons can only be applied to total purchase, not individual items. Make sure your discount does not exceed the cost of your lowest-priced item.