find a piece of soft dry wood
fashion a plowing stick from the samepiece of wood (using a sharp rock)
Grip the plow with both hands and push back and forth. When a fine wood dust begins to accumulate, continue faster and with slightly more pressure, focusing on building up a neat little pile.
When the pile is smoking on its own, that means you've got an ember burning
and it's ready to be transferred to your tinder bundle.