If you are attempting to print a label to your printer without using Automatic printing or downloading the label as a PDF then you will need to print the label using the "Print to X" option in the shipment options menu.
If your printer is not showing up you will first need to make sure your printer is able to connect to Shiptheory by checking if you have the Shiptheory print client. If you don't have this you can refer to our Automatic Printing Guide which includes the instructions on how to download and set-up the print client.
If you do have the Shiptheory print client then you will need to add your printer to the list of available printers to print on. This can be done by going to the Printer Configuration page and scrolling down to the "available printers" page where you can add the specific printers you want to print labels directly off of. Once the printers have been added you will be able to directly print the labels off of that printer from the dashboard page.
If you are still unable to print please don't hesitate to contact support.