Since the discount Lists module is primarily designated for companies to whom you want to provide discounts, there is a specific relation between the Discount Lists module and the Companies module.
Suppose that you have these discount lists in your list:
If you want to relate a discount list to a particular company, you do it in the Company window where you click the Discount List field. There you can choose the discount list you want to apply.
This is a general discount that will be applied to all products that you relate with the company as a customer. During the creation of a bookkeeping record, if you select a company that has a certain discount list, all new products added to the bookkeeping record will bear this discount. The discount will apply only to new products, not to products that were already in the bookkeeping record before you selected the discount list.