The Discount Coupon itself appears in emails you send to customers ...

Customers can test their Discount Coupon Code from the link in the Information sidebox ...

And Discount Coupons are accepted during the checkout ...

If you want to make them and have them just display on your site as extras for your customers ... you might consider adding a new page via EZ-Pages ... assuming that you are Zen Cart v1.3.x ... and post the Discount Coupon codes there for the asking ...