Using up-sells and cross-sells, you can cross promote your products. They can be added by searching for a particular product and selecting the product from the dropdown list:
After adding, they are listed in the input field:
Up-sells are displayed on the product details page. These are products that you may wish to encourage users to upgrade, based on the product they are currently viewing. For example, if the user is viewing the coffee product listing page, you may want to display tea kettles on that same page as an up-sell.
Cross-sells are products that are displayed with the cart and related to the user’s cart contents. As an example, if the user adds a Nintendo DS to their cart, you may want to suggest they purchase a spare stylus when they arrive at the cart page.