You need to make settings on the printer or the printer driver to use the Staple Finisher when printing.
Select in the following order on printer's control panel.
If you select Auto, the printout destination is set to the finisher tray.
When printing from a computer, you can specify whether or not to use the finisher tray from the Output Tray menu on the printer driver. If you select Auto Select, the printout destination is set to the finisher tray.
Even if you make settings for the printout destination on the printer's control panel or the printer driver, they may not be applied depending on the paper size or the paper type. Instead, the printout destination might be automatically set to the output tray, the face down tray, or the top output tray.
When using the finisher tray, do not remove your printouts while the print job is still in progress. The print position may be misaligned and the staple position may move from its original position.