Coupons are applied to all eligible items in your inventory unless you have specifically excluded them from being discounted.
You can advertise your coupon with a site-wide message.
Click on the 'Electronic Coupons' link under the 'Commerce' heading in the Control Panel menu. Then, click 'Add a New Coupon.'
From there, you can add the coupon details including the coupon information, type, restrictions, etc.
When you are finished adding the coupon details, click the 'Submit' button at the bottom of the page.