Tiles Overview

Windows 8 tiles interface has an overview mode. Many apps incorporate this view, which can be accessed through a small set of +/- buttons on the bottom right corner of the screen. Once in overview, you can typically click on a 'set' or tile (depending on the interface used when developing the overview) to focus on that particular area of the app.

BBC News Overview Snippet

Different apps may include the overview in different ways to others, for example the default weather app will provide a list of tiles explaining the section they lead to, as oposed to the graphical tile interface used by the BBC (screenshot).

Along with the overview, some apps make use of the +/- keys to provide other functions, for example viewing an image in the default gallery app makes use of these buttons for zooming in and out.

Give it a shot, the first play you'll see these buttons are on the start menu.