These classifications can be used however best they fit into your product organization. Typically, Product Groups are a way to organize a group of similar products, such as “Soft Drinks”, “Watches” or “Collections”. Product Brand is used to define the brand name of the item (example, Del Monte, Purina, Timex, etc.). Tags can be used to further define products such as by year, event, or industry. You can add Product Group, Product Brand and tags from the Organization tab in Edit Product.
Product category corresponds to QuickBooks categories.