Click in the white box and type what you want on the label. It prints at 51 mm × 25 mm.
Printing on the Zebra ZD230
First time only: in Windows, open Printers & scanners, pick the ZDesigner ZD230, then Printing preferences. Under Page Setup create a new label size of 51 mm wide by 25 mm high, portrait, and save it.
Each time: click Print label, choose the ZDesigner ZD230, then under More settings set the paper size to your 51 × 25 mm label, margins to None, scale to Default (100%), and untick Headers and footers.
If the print is pale or patchy, turn up Darkness in the same printing preferences. If it starts part-way down a label, hold the printer's feed button to recalibrate.