You can create fixed value discount coupons or percentage discount coupons. There is also a special coupon to provide base price discount - this voids you of any profit, and is suitable for you when buying your own products.
You can manage coupons simply by going to "Selling" >> "My Coupons".
With either fixed or percentage coupons, the actual discount is taken from your profit and you cannot provide a discount below the base price. Each coupon can also be set up to expire on a particular date. Each coupon can also have a minimal order price - such coupon can only be used on orders whose total exceeds the minimal price. It should also be noted that only one coupon can be used per order.
Where do my clients enter the coupon code? As long as you have at least one valid coupon, your customers will see an "Enter Coupon" field in their shopping carts at the top of the cart section listing the products to be bought from you.
You can create a 15% discount coupon with the expiration date set at 1/1/2013.
You can create a $5 discount coupon on all orders above $30 with the expiration date set at 1/6/2014.
What can I do next? To offer your clients discounts you may consider creating packages and offering full-album downloads at a single price.