The app has three key use cases as described by the Windows Phone Blog:
- Finding content - allowing you to browser and search the Xbox LIVE Marketplace.
- Find out more - when playing content you can get additional information (e.g. actor information when watching a movie).
- Control and play - controlling content playback, effectively acting as a souped up remote control unit.
The app can be seen in action at around the one minute mark of this video.
The Xbox Companion app is described as 'coming soon' and will be available for free from the Windows Phone marketplace.