Your Macintosh should be shut down, not just turned off. To shut down a Macintosh, switch to the Finder and choose the "Shut Down" command from the "Special" menu.
You can also press the power key on the keyboard to shut down the computer. Pressing the power button displays a dialog box with options to restart, sleep, cancel, or shut down the computer. Click the button of your choice.
Figure 1, Shut Down command
You can also press the power key on the keyboard to shut down the computer. Pressing the power button displays a dialog box with options to restart, sleep, cancel, or shut down the computer. Click the button of your choice.
Figure 2, Shut down dialog box
During the shut down process, your Macintosh quits all open application programs. If you have not saved your work, most applications will give you the opportunity to do so during the shut down process. After all applications have been quit, the Macintosh turns itself off.