When an order ships, ShipStation notifies your selling channel that an outgoing shipping label was created, including details about the shipment (such as the tracking number and the shipping provider). You can delay this marketplace notification based on certain criteria if that makes sense for your business process. And even if you ship an order outside of ShipStation, you can still "Mark Orders as Shipped"-- we'll send your selling channel shipment notifications for these as well.
The only thing that ShipStation communicates back to your selling channel are the shipping notifications mentioned above.
Since ShipStation has so many features, this may come as a surprise-- especially to new ShipStation users. This is because many functions (like canceling orders, modifying internal order notes, and deciding the shipping services exposed during the checkout process) are best handled outside of ShipStation.