Printer Setup is covered on pages 17-19 in the AirPort Express 802.11n (1st Generation) - Setup Guide , which was supplied with your AirPort Express.
The basic steps are as follows:
- Connect the printer to the USB port on the AirPort Express using a USB cable and make sure that both devices are powered on.
- Open System Preferences (gear icon on the dock) and then open Print and Fax
- Click the small + (plus) button at the bottom of the printer list on the left
- Hopefully, your printer or printer family will appear in the next window
- Click the name of the printer to highlight it
- Click the Add button at the lower right to install the printer at the AirPort Express location
- Try to print.
You will need to be sure to select the correct printer "location" at the AirPort Express. If you previously connected the printer to your Mac, it will appear as if you have two of the same printers.
Closer inspection will reveal that you have a printer installation at the Mac location and a printer installed at the AirPort Express location. You must choose the correct AirPort Express location to be able to print
Printer troubleshooting is covered on pages 33-34 if you need more tips