In order to create discount codes for your products/services login to your main Eco Web Hosting account and then go to
Reseller Services: Your Greenhost Shop > Discount Codes.
From this page you can configure the name of the code (ie. the code to add in the basket), the discount amount (in your currency or a % discount) and an expiry date if this is a short-term offer:
Below these options you will have a list of your products (these are a demo in the screenshot below) to allow you select each of the products that you want this code to apply to: