Do you have a need to discount a particular product variant in your store?
First, go to Promotions | Discounts and click Add New
Give your Discount a descriptive name
Choose Discount Type: Assigned to product variants (SKUs)
Either give a discount percentage or dollar amount.
Choose Start and Stop dates for the discount code.
Check Requires coupon code.
Enter your coupon code unique id
Enter your limitations for your discount/coupon.
Go to Catalog | Products | Manage Products and Edit your product to be discounted.
Click Product Variants and Edit the variant to be discounted.
Click the Discounts tab and select the previously created Discount.