Quick Mac tip for Apple users!
If an app becomes unresponsive, press Command-Option-Esc to bring up the force quit application box; much like Control-Alt-Delete on a PC.
Simply select any app from the “force quit application” box and click on force quit.
If the app still does not quit, you may need to take it one step further.
If all else fails, search for “Activity Monitor” on your Mac and open it. Once open search for the app you wish to quit and right-click on it for an option to force quit application.