Drafting is the main motion of spinning. It's a simple process really. You are stretching/thinning the fibers from each other length wise so that the ends can grab and twist, thus creating yarn. It's like pulling the fiber strands apart, but not all the way.
The following is an example of drafting off the wheel. Please forgive the terrible drawings :)
Here is it in real life.
A length of roving.
Pulled apart almost in half, but notice that the fibers in the middle still overlap.
In the next post I'll apply this concept to the spinning wheel.