1. Drawing
DRAWING BY ERASING

2. Drawing by Erasing
Drawing by erasing involves 'drawing' the lightest areas of a pictures with an eraser (working in the reverse).
You would begin by darkening your paper by adding layers of charcoal.
Instead of using a pencil to build up layers of shading, use a kneaded eraser to gradually take away the highlights. 

3. Drawing by Erasing
The key is to take a little bit of charcoal away at a time.   
You would not just draw with your eraser.
The goal is to work back and forth with your eraser and your charcoal to create the perfect values.