With the introduction of the Metro interface in Windows 8, there are now two distinct types of windows: Apps and traditional desktop windows. Since Metro is designed for both touchscreen and mouse input, the methods for closing apps is...
Method 1 of 3:
Closing an Open App
Close an app using your mouse. If you are using a mouse, you can close the app much like you would a desktop window. The app may prompt you to save your work before closing.
Close an app using your finger. If you are using a touchscreen, drag the app from the top of the screen to the bottom. The app will close and you will be returned to the Start screen.
Use the task bar. Move your mouse to the upper-left corner to display a list of all your open apps. If you are using a touchscreen, swipe in from the left side of the screen.[1]
Press .Alt+F4 to close the active app. This is useful if the "X" is hidden, the app is frozen, or you can't figure out how to make the onscreen controls appear.
Method 2 of 3:
Closing Windows in Desktop Mode
Click the "X" in the upper-right corner. This will immediately close most windows in desktop mode.
Right-click on the window's icon in the taskbar and select "Close window". The taskbar is located at the bottom of the screen, and open windows will have highlighted icons.

Press .Alt+F4 to close the active window. This is useful if the "X" is hidden or you can't move the window.
Method 3 of 3:
Force-closing a Window or App in Desktop Mode

Press .Alt+F4 to force close the active window or app. This will work for windows in desktop mode as well as for Windows 8 apps. This is a useful shortcut for frozen programs that aren't responding to clicking the "X".
Press .Ctrl+⇧ Shift+Esc to open the Task Manager. This will open a list of all your running processes, and is the easiest way to close any non responsive programs. By default, the Task Manager will open displaying the Processes tab, which shows all of your open apps and running processes.Update 04 March 2020
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