Here you add and edit individual pie slices.
To edit a pie slice name and value, tap on the slice cell.
Tapping the "+" button adds a new slice named "Unnamed" with value 0.
Tapping the "Edit" button enters the edit mode allowing to delete selected slices.
The iPhone image on the left is live. You can click with your mouse on the buttons to navigate from one view to another, like on a real iPhone.