There are two ways to sell products on your WSN site:

1. A shopping cart where people buy products from you
2. Classifieds where submitters list their own products and payment buttons and visitors buy from them

Once you switch on sales at Admin -> Settings -> Switches, there will be a settings page at Admin -> Revenue -> Sales Settings. On top of that page, your first choice is which of the two above types of sales you'd like to do. For more information on either type of sale, click the type above.