Coupons are pretty easy and have really nothing to do with FoxEE other then the coupon entry and discount will show up in your cart through the JSON communication.
Log into your FoxyCart account, create a new coupon following their instructions. all of the coupon settings will be available for the products in the category you select. When a customer goes to add that product to their cart the coupon option will be available. They can then enter the coupon code you provide and the price will be calculated to reflect the type of discount you provided.
One thing I did notice is that in the HCC store the side bar cart didnt show the discounted price, but I believe that is cause during testing I didn’t update the template to display the right info.
Hope this helps