Can't turn off iTunes on MacBookAir
There can be multiple things happening here. If you have the spinny wheel, iTunes is obviously hanging/not responding. You can fully quit it by using Option + Command + Escape, selecting iTunes, and pressing Force Quit. If that doesn't work, you can open Activity Monitor (You can press Command + Space and then type Activity Monitor), find and select iTunes, and press the Stop symbol with an X in the center, and that should be the end of that. If none of this works, you can restart.