The Links tab specifies which pages OpenCart will show the product on:
Manufacturer: Selecting the product's manufacturer will place the product on the manufacturer's page. Select manufacturers can be viewed on the home page if added to the manufacturer banner.
Categories: Check the categories that the product will be placed into. The product will be listed on the category's page in the store.
Filters: Select the filters to be applied to this product if your Filter module is enabled. See Filters for more information.
Stores: Check which stores will sell this product. Clicking "Default" applies if there is only one store to be managed.
Downloads: If the product is a downloadable product, select the file that will be included with the purchase.
Related Products: In this space, type any related products for this product. These products will be displayed on that product's page for the customer to view. When typing in the space, a drop down box will appear with related products.