Summarize:

You'll need to be connected to the same network as the printer to print wirelessly. You can print files from Google Docs, Drive, your web browser, and virtually any other app. It should be at the top-right corner of the screen. This is where you'll find the menu in a lot of Google-specific apps, although other apps may display a different menu icon and/or location. This displays the print preview screen. If you see anything other than the printer you want to use selected at the top-left corner of the screen, tap the menu and choose your printer. This sends the selected file to the wireless printer.
Connect your tablet to the same Wi-Fi network as the printer. Open the file you want to print. Tap the three-dot menu on the open file. Tap the Print option. Select your printer. Tap the yellow printer icon to print.