Kill a misbehaving program
If an application/program is frozen or using up all of your CPU cycles you need to get rid of it. Of course, you prefer not to do this because any unsaved documents in the application will lose their latest changes but sometimes there is no choice.
In Windows you do this by bringing up the Task Manager with Alt-Control-Delete, select a running application (or a process if you are adventurous), and have it terminated.
On the Mac the Activity Monitor is similar to the Task Manager but there is a simpler way to get a misbehaving program to stop: with Force Quit. Bring up the Force Quit window either from the Apple menu -> Force Quit… or with the keystrokes: Command-Option-Escape. Select the application to stop and click on the Force Quit button.