There are few options to connect a printer to NextD:

1) Install your printer's own Android app on NextD

2) Install a 3rd party Android printer app such as "Mobile Print" and "PrintEasy".

3) If your printer supports Google Cloud Print, you can install the Google Cloud Print app on NextD to connect to your printer.

In any case, your printer is required to have a WiFi or Bluetooth connection. Most newer printers should have these as standard features.