If you have set your Shopify integration to process your Shopify orders, Shiptheory will fulfil your orders to create a Shopify shipment in order to book the shipment with a courier.
When setting Shiptheory to process your Shopify orders, you will have selected an Inventory Location in Shopify from which Shiptheory should look to fulfil your orders. When Shiptheory processes your order, each stock-tracked item in the order is checked to see if it can be fulfilled from your selected inventory location. All items that are stocked in the selected location along with any non-stock-tracked items are then requested to be fulfilled.
More information about Stock Locations is available from Shopify here: https://help.shopify.com/en/manual/locations
If you have any further questions about Shopify orders, shipments or anything else, please don't hesitate to get in contact with our support team.