When your Mac isn't frozen but is just running slowly or acting strangely, and shutting down some programs to free up memory doesn't solve the problem, try a restart. A restart turns your machine off and then on again. (You may also need to restart after you install a new program.)
Here's how to restart your Macintosh:
Click the Apple menu. A pull-down menu appears.
Select Restart.
You can also restart your Macintosh either by pressing the power button once or by pressing ctrl and the eject key. The eject key appears in the upper-right corner of the keyboard, above the delete key. The eject key displays a symbol of a triangle with a line underneath it (see Figure 1-3). When a dialog appears (see Figure 1-2), click Restart.