How to Print barcodes on Zebra or Dymo printers

You should create the custom page size that is equal to your media size first.  Say 1" x 1.25”, and use the File>Page Setup menu option for that, or use the standard Page Size for your printer:

Then create a custom label format 1" x 1.25”,  1 across, 1 down. For this, Click on the Custom tab above the Label Formats list, and click the Add button :

After that, you can print your labels. Select File>Print, and if necessary, set the desired quantity using the Labels From: and  To: values from the Print panel :