In the WooCommerce admin area when you are editing the product data there is a “Linked Products” tab. Products can be related to each other in three ways: Up-Sells, Cross-Sells, or by having the same tags or categories.
Up-sells are products which you recommend instead of the currently viewed product, for example, products that are more profitable or better quality or more expensive. Depending on your site’s template these products will display on the single product page underneath the product’s description.
Cross-sells are products which you promote in the cart, based on the current product. Depending on your site’s template they will display on the cart page underneath the cart products table with a thumbnail image.
Related products is a section on some templates that pulls other products from your store that share the same tags or categories as the current product.
These products can not be specified in the admin, but can be influenced by grouping similar products in the same category or by using the same tags.