The Auto-Remove Background Tool is great when you have a product shot on a relatively solid-colored background and has a high contrast to the product (ex: light background with a dark product).
Product image before adding to the Products library
Product Image in the Editor’s Auto-Background Removal Tool Panel
If the product is shot within a space where there is a lot of color variation, you will need to use the Manual Remove Background Tool to trace around the item and remove it from the background.
Product Image having multiple color variation as its background
Product Image in the Editor’s Manual Background Removal Tool Panel
This option works a lot like the Pen Tool in PhotoShop. To know more about the Manual Background Removal Tool, click the links for the appropriate video tutorial and help article: