What is the first step in teaching someone how to ski?
Teaching someone to do anything starts with understanding how they learn.  Does the person learn by listening, reading, watching or doing (trial and error).  Most people learn via a combination of the above.  Let's assume the trainee learns via watching and doing.  The first step is safety.  The instructor must teach the basic stopping mechanism.  Once the trainee can stop this will provide a measure of confidence and instill with the trainee that they are in control and will be able to stop at any time.  The basic stopping mechanism is something called a pizza-pie or wedge move.  The tips of the skis are positioned together (barely touching) with the back of the skis much further apart.  As far apart as the persons hips or even further.  The further apart the back of the skis are the slower the person will go to the point of stopping.   The trainer should both describe and demonstrate this position to the trainee.  The trainee will copy the position with feedback and adjustments from the trainer.  Practicing this formation should be done many times until the trainee is comfortable stopping on steep slopes.  Once this effort is mastered, the trainee can move to the next steps in learning how to ski.