Use the correct key or switch to power the device on
If it is a light or lamp, flip the wall switch to the on position
If it is an appliance, press or toggle its power button
If it is a circuit or breaker, move the breaker to the on position
If it is a gas valve, turn the handle so it is parallel with the pipe
If it is a water valve, turn the handle counterclockwise to open it
If it is a software setting, change the toggle from off to on
If it is a knob or dial, rotate it in the direction that increases the setting
If it is a lock or latch, turn or move it until it engages
If you mean “how to turn on,” specify the object for exact steps