It seems you do need to install something - see the manual:
Once connected and booted up, you can navigate to the terminal to install the required
In RetroPie, you can do this by pressing the Ctrl-Alt and F4 key; this changes view to a
virtual terminal window, which you can run ‘emulationstation’ to go back to
It looks like you need to install GPIONext, a GPIO user driver to make the gamepad(s) work.
my controller has a D-pad, a left analog stick, and a right analog stick. I would like all three of these to act as movement controllers when in the NES emulator.
You can mirror the DPad the the left or right joystick for the NES specifically by adding:
input_player1_analog_dpad_mode = "1"
for the left stick, or:
input_player1_analog_dpad_mode = "2"
for the right stick to /opt/retropie/configs/nes/retroarch.cfg. To mirror the DPad to both sticks at the same time, as well as your other requests, you'd need to employ an external mapping solution such as Linux Joystick Mapper or xboxdrv.