The Top N products by sale web part displays the top N best-selling products. The best-selling products are chosen according to the frequency of their occurrence in customers' orders, not according to the total volume of sales. For instance, if a customer buys 10 items of the product A and 2 items of the product B and a second customer buys 4 items of the product B, the product B is evaluated as the best-selling.

The web part is not displayed by default as there are no customer's orders in the standard installation of the Sample Corporate Site. If you wanted it to become visible on this page, you would have to create an order (go through the shopping process) in the Products section of the site.