The Live Calendar tile shows you an overview of the coming appointments from the account you are logged in with. By clicking on the "+" icon you can quickly set an event.
Fromt the live tile, you can see detailed appointment information when you click on a appointment. From the bottom you can open the Calendar.
To activate the app:
Change the tile format to 4 x 4 to get live version.
When changed back to 2 x 2 or 1 x 1 format it will show the regular icon.