A product is the item you are selling from your own inventory or a dropship supplier's inventory. A listing is the location on your storefront where your customers view and purchase the product. Therefore you may have 1 product with more than 1 listing. For example, you may have a coffee pot in inventory that is being sold on Ebay, Amazon, and Walmart simultaneously.
Products can be viewed by navigating to Products > All Products. Here you can add manually edit quantities for your items and add new products into your inventory.
Listings can be viewed by navigating to Products > Active Listings. Here you can update listing information for active listings such as Title, Price, Description, etc.