There are two eCommerce solutions, native store and third party eCommerce. If you are in the platform and are unsure about which solution you are using you can check two places, the top of the Commerce panel and the Store Management menu.
To check which solution you are using, in the side panel, click Sell Online. This opens the Sell Online panel. At the top it will be labeled either Native eCommerce or Third Party eCommerce.
To check the Store management menu, click Sell Online. If there is a menu option Store Management, then you are using native store. If there is a Manage Store button to access the Store management menu, then you are using third party eCommerce. Pictured below are the two Store management menus.
Native eCommerce store management menu
Third Party eCommerce store management menu