How to Close a Windows 8 Modern UI AppBy: Arie Slob
When you start any of the new Modern UI ("Metro") apps, you may be left wondering how to close it. During the development phase of Windows 8 there was no easy way to close an app, but Microsoft gave in to pressure and added a way to close any opened app... except you'll have to know how. There's no close button, instead just move the mouse cursor to the top of your screen where your cursor will change to the icon of a hand. Click and hold down the left mouse button to "grab" the open application, drag the app to the bottom of the screen, and release the mouse button. This closes the app.
You can also close an app using the keyboard shortcut Alt + F4 from within the open app, but not all apps support this. Another option is to access the switch list by pointing to the top left corner of your screen with the mouse and right-click the app you want to close (Figure) . You can also use Task Manager to close apps.
Microsoft designed the apps to keep running in the background using minimal system resources, so that apps that you have launched are available at a moment's notice. You can see from Task manager how much resources your apps use. In the screenshot you'll notice that I have opened four apps (Maps, Messaging, People and Weather) and together they use 3.5 MB of memory.