Tap the Start button on the controller to wake it up -- there is no on/off switch, but that's OK, the battery should last about six months between charges thanks to deep sleep mode.

Pair it with your computer or mobile device in the Bluetooth settings.

Use a gamepad tester, such as https://hardwaretester.com/gamepad to check the buttons are all working as expected.

In your game or emulator, map the controls however you like.

Have fun!