For parcel sized shipments, when you process the shipment thru ShipStation they will get an automatic email with tracking info. For the larger shipments the Buyer is the one that selects the shipper.
When you move the status of the order to "Ready to Ship" and process it through ShipStation the Buyer will be sent a notification as well as any requisite tracking information.
For the Big and Bulky and Crated & Palleted orders the Buyer will initiate the shipping process. Through Uship or their own shipping partners coordinate the shipping process. As the Seller all you will need to do is tell them when the order is ready for pickup