To turn on a computer you would either push and/or hold the power button.
To then turn it off, you can either push and/or hold the power button. Or for a lot of computers, most actually, if you go to the start icon which should be located on the letf along the bottom of the screen if you have a pc, and if you click it there should be icons on there that say "Log Off" and "Turn Off", so select "Turn Off" and it will say Restart, Standby, and Shutdown, so pick one, click it, and that's it.
Good luck
To then turn it off, you can either push and/or hold the power button. Or for a lot of computers, most actually, if you go to the start icon which should be located on the letf along the bottom of the screen if you have a pc, and if you click it there should be icons on there that say "Log Off" and "Turn Off", so select "Turn Off" and it will say Restart, Standby, and Shutdown, so pick one, click it, and that's it.
Good luck