When you stop using an app, Windows leaves it running in the background and then, after a while, closes it for you.
To close an app yourself, drag it from the top of the screen to the very bottom. If you're using a mouse, move your mouse pointer to the top of the screen and then click on the Close button in the title bar.
To completely stop all processes associated with an app, drag the app to the bottom of the screen, and hold it there until the app flips over.
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