Cross Sales provide the ability to link similar products to increase their visibility on your web site. Just like a brick and mortar retailer will display bikes, and bike accessories in the same area, cross sales allow you to display the items together on your site.
Cross Sales can be included anywhere there is an identifiable product. The most common uses are on the Product Detail page and on the Shopping Cart page. Department pages usually do not display Cross Sales because there is already a large selection of related products on display.
Cross Sales can be shown on your site in any number of ways as fits your products and page layout. How they are displayed is determined in the design phase.
Refer to your site documentation for how cross sales are implemented on your site.
Cross sales can also be setup as part of your product configuration.