ShipStation makes it really easy to create a SCAN form for your USPS labels. You'll start out at the Shipments tab.
Next, click the End of Day section on the sidebar.
The "Open" section will show by default, and it will display an "Open Shipments" count for the selected day. If there are no open shipments for the selected date, you can click the calendar icon to select eligible USPS shipments with a future Ship Date. (Please note that USPS guidelines prevent you from creating SCAN forms for shipments with a Ship Date in the past.)
When you're ready to put any open Shipments on a SCAN form, click on the Close Shipments link corresponding to the USPS carrier.
A new window will appear where you can select (or deselect) the shipments for your SCAN form. Furthermore, if you only want to close shipments for one of your Ship From Locations, click the all Ship From Locations dropdown at the top. From there, you'll be able to close only a particular Ship From Location's shipments.
Just click Close Selected when you're ready. Your forms will be created and you can print from this popup!
If you want to print (or re-print) SCAN forms that you previously created, click on the Closed section (under End of Day), and change the "Ship Date" filter (or the "Closed Date" filter) as needed.
Once you do that, you can check boxes corresponding to any SCAN forms you want to print, and then click the green Print Selected button to the top right of the End of Day list.