A hallmark of the new apps that ship with Windows 8 -- including Mail, People, Weather, Music, Bing, Photos, Maps and others -- is that they're designed to run in full-screen mode, and they don't display menus or toolbars. But if you right-click anywhere in the app, an App bar appears at either the top or the bottom of the screen, or both.
The options available in the App bar vary according to the app you're running and what you're currently doing in that app. In the Weather app, for instance, the App bar lets you refresh the page, change between Fahrenheit and Celsius, navigate to other places you've chosen to display weather, and so on.
Back to Windows 8 cheat sheet