You have what Huion called Press Keys or express keys on the side of the Tablet or Tablet Monitor. For example, I would set one of my keys to a keyboard shortcut B for using the brush and another for G for the bucket tool, etc.
They are on the top side of the tablet window and are programmable for shortcut keys.
Because the tablets are usually black, and the buttons are also black. In a dark room (early morning for example), it is hard to see the buttons.
So I painted a white dot on each button.