RW Elephant allows two types of discounts. The first is Percentage Discounts which allow you to take a percentage off the total of an order. The second is Flat Discounts. These second discounts allow you to take a flat dollar amount off the invoice rather than a percentage. It basically acts like any other fee except that it uses a negative number rather than a positive one.
Discounts are for variable amounts you want to reduce the order by. You would use a Discount to reduce the invoice total by $300 for instance. They can be taxable or nontaxable (meaning they reduce the total before or after sales tax is calculated).
Create a Flat Discount just like you would any Conceptual Item. The only difference will be in the "Rental Price" field; you'll enter a negative number instead of a positive one.
You can change the "Unit Price" of any of these Discounts as you need to on a particular Order.
Also see: Percentage Fees & Discounts