The CommandBar control is a general-purpose, flexible, light-weight control that can display both complex content, such as images or text blocks, as well as simple commands such as AppBarButton, AppBarToggleButton, and AppBarSeparator controls.
XAML provides both the AppBar control and the CommandBar control. You should use the AppBar only when you are upgrading a Universal Windows 8 app that uses the AppBar, and need to minimize changes. For new apps in Windows 10, we recommend using the CommandBar control instead. This document assumes you are using the CommandBar control.