How to Close Running Applications on the Mac 

Mac and Windows differ in the way they close apps. On Windows, the app shuts down when you close the app window. On macOS, a window is just one instance of the app. So, when you select the Close button, the window instance disappears, but the app stays open in the background. You can check which apps are open from the Dock; those icons are marked with a tiny black dot. 

To explicitly shut down an app (that is, completely close it), you must use the Quit command.

Use the Menu Bar to Quit an App

Quit an app so that it doesn’t reopen when you restart your Mac.

Go to Menu Bar > App Name > Quit.

Quit a Closed App From the Dock

Closed apps will have a black dot below their icons. Quit apps when you aren’t using them.

Dock > Right-click on App > Quit.

Quit an App With the Keyboard Shortcut

Use this shortcut on a single open app or use the application switcher on several apps.

Press Command + Q to quit the open app.  Use Command + Tab (shortcut for the Application Switcher) to switch to another open app and then select the Q keyboard shortcut while keeping the Command key pressed.  

Use Force Restart or Shutdown to Close All Apps on a Mac

Restarting the Mac or shutting it down to start afresh may be the only way to take back control when multiple apps stop responding and force quit also doesn’t work. Follow these steps to restart or shut down your Mac. You can also Force Quit from the menu.

Go to the Apple Menu > Restart or Shut Down. A dialog box appears asking if you want to reopen your windows when logging back in. Uncheck that option if you want to start again without the app(s). If the restart and shut down option doesn’t work from the menu bar or the menu bar itself is unresponsive, force restart or force shutdown the Mac from the menu or the shortcut keys below. Force restart: Press the Command + Control + Power button together till the screen goes blank, and your Mac restarts.  Force shutdown: Press and hold the Power button until your Mac powers down.

Should I Quit Apps on the Mac? 

Make it a habit to quit apps that are no longer in use. Closed apps keep running in the background and eating into the system resources. They can cause macOS to slow down and cause some apps to freeze or not open at all.

Force restart: Press the Command + Control + Power button together till the screen goes blank, and your Mac restarts.  Force shutdown: Press and hold the Power button until your Mac powers down.

When apps freeze and stop responding, you can force quit the macOS app but take the risk of losing unsaved work.

What About the Red Crossed Button to Close a Running App?

Using the red Close button (the button marked as an X) on the top left corner of the application window only closes the current window open in an app. The app remains running (even if there aren’t any open windows associated with the app).