To turn the computer on, place the Power switch in the "On" position.
To turn the computer off, place the Power switch in the "Off" position.
If you leave the Power switch in its current position, the computer will remain on if it is already on (Power switch in the "On" position) or off it is already off (Power switch in the "Off" position).
If the computer is unplugged, the Power switch has no effect. However, if the Power switch is placed in the "On" position while the computer is unplugged and the computer is subsequently plugged in while the Power switch remains "On", the computer will turn on at the time the plug is inserted.
See also: Switches: Operation of, The Power Plug, On Mode, Off Mode.