After you finished adding your carrier. Go into Orders -> New, there is the “Action” column where you will find the “Ship Order” button.
Press the “Ship Order” and in the new pop-up window select your courier (we're using Royal Mail as an example here).
Then enter the package details or choose a Package Preset, any additional features you may require like Signature or Insurance (options will vary depending on the carrier you're using), and finally your Courier Service. Then simply press Buy Shipment(s) and your label will be booked and your Sales Channel order status updated with courier information like the Service Used and Tracking Code.
After pressing Buy Shipment(s), the window will change to allow you to print your Shipping Label, Invoice, and Other documents you may need.