Apple's iMac computer is a user-friendly model that starts up and shuts down quickly with minimal effort from the user. The power button for the iMac is located on the back, left side of the computer. You can force a shut down if your computer does not respond or the system hangs, but for everyday use, shutting down your iMac is a function completed within seconds from the Apple Finder menu.
Click on the "Apple" menu on the Finder Menu. Scroll down to "Shut Down."
Confirm you want to shut down your iMac by clicking on the blue "Shut Down" button in the dialog box that pops up, or do nothing and allow the system to automatically shut down the iMac in 60 seconds.
Alternately, force the computer to shut down if it is unresponsive by holding the "Power" button down for at least five seconds, then release.