Mac OS X provides several ways to control open applications.
You can switch among open applications by clicking the icon of the open application to which you want to switch on the Dock or by using the +Tab or Shift+ +Tab keys (the currently selected application's icon will be highlighted on the Dock as you press the +Tab or Shift+ +Tab key combination). If the Dock is hidden, it will appear when you use these keys.
Hide applications quickly by pressing +H or by choosing the Hide command on the application's Application menu.
Quit an open application by holding down the Control key while clicking the application's icon on the Dock. From the pop-up menu, choose Quit.
There are several ways to force a hung application to quit. Press Option+Command+Esc to open the Force Quit Applications window, choose the application you want to quit, and click Force Quit (see Figure 8.9). (If an application is hung, its name will appear in red in the Force Quit Applications window.) Open the Process Viewer application (Applications/Utilities), select the application you want to quit, and choose Processes, Quit Process (or press Shift+ +Q). Use the Unix kill command along with the process number of the application you want to force to quit.
When you select the Finder in the Force Quit Applications window, the Force Quit button becomes Relaunch?the Finder must always be running when you are using Mac OS X.
To learn more about the Process Viewer, see "Using the Process Viewer to Understand and Manage Processes," p. 817.
To learn more about using Unix commands, see Chapter 9, "Unix: Working with the Command Line," p. 213.