The app automatically categorizes products into groups based on fulfillment services.
If you have fulfillment services set-up ( either manually or automatically by an app ), you will see those fulfillment services appear in the app within the Product Groups tab, as a top level product groups.
If you change the fulfillment service of a product in the Shopify admin, that product will automatically be assigned to the Default group for that fulfillment service.
If you assign a product from one fulfillment service to a group belonging to a different fulfillment service, the app will reassign that product to that fulfillment service.
When you create a new fulfillment service in your shop, you must go to the app's Sync tab, and click the Sync Fulfillment Services button to have that fulfillment service appear in the app.
What is a fulfillment service?
A fulfillment service is a third-party warehouse or vendor that prepares and ships orders for you.
Some examples of fulfillment services, that have integrations with Shopify are Fulfillment by Amazon, Shipwire, and Rakuten.
But there can also be custom fulfillment services that you use for dropship vendors or other providers of products to your shop.
Shopify offers some basic functionality for custom fulfillment services — mainly sending an email to a vendor of only the products in an order that belong to that fulfillment service.
These can be created, edited, and viewed by going to Shopify Admin > Settings > Shipping > Accounts and Integrations > Manage Integrations