Press Command + Option + Esc
Select the app you want to quit
Click Force Quit
If the app is frozen and the menu is accessible, click the app name in the menu bar
Choose Force Quit
Open Activity Monitor
Select the unresponsive app
Click the Stop button
Choose Force Quit
Press Command + Option + Esc
Use the keyboard to select the app
Press Return to force quit
Click the Apple menu
Choose Force Quit
Select the app
Click Force Quit