Treatment labels can be printed when you add a treatment to an animal's record. When you're adding a treatment to the animal's record from the Treatments subtab, you'll see this pop-up to complete:
At the very bottom of that pop-up, you'll see an option for "Create printing label". Checking that box will trigger a few additional fields to complete. These fields will be additional information that displays on the label.
Once you've completed all fields and clicked "Save", a new tab will open in your browser for the label. To print the label, click the small "Print Label" button in the top right corner of the tab. Before clicking print, just make sure that you've selected your label printer and have it configured with the correct paper size. Currently, the printouts are 2" tall and 3" wide by default, which is the recommended size label to purchase. (Labels will expand in height if the text entered into the Additional Label Notes field extends beyond the printable area.)