A product refers to the broadest classification of the goods that make up your inventory.
Example
If you sell clothing your products would consist of shirts, dresses, shorts, etc.
Products can then be further broken down into variants and in some cases bundles.
You can upload products both individually or in bulk via CSV.
After you import your products onto QuickBooks Commerce, you will be able to view and manage your products via the Inventory section.

Learn more about creating and managing products with these handy articles:
How do I Create a New Product?
How do I Upload Products Via CSV?
How do I Edit Products in Inventory?
How do I Delete Products in Inventory?
How do I Enable or Disable Products in Inventory?
How do I Add or Remove Bin Locations?
How Do I Create A Product That Does Not Need Stock Management?