I used to teach swim lessons and until they are 1-2 years old, it is simply about getting them used to the water so it is not a scary place to be. I purposely spray water over my 6mo old's face in the tub so she will be used to it. Good for you to sit with him on the pool steps and kick. He will watch you and if you are having fun in the pool, so will he! Make up silly games and songs and have fun.
I taught private lessons to 2year old twins last summer and they learned to float with help getting started and they could "swim" a distance of about 4 feet. I do NOT recommend floaties b/c they alter the body position in the water (teaching incorrect balance) and provides a false sense of security. You should be with him at all times in the pool. Noodles are a better option--tuck across chest and under arms and let him float in a prone position (on tummy)...progress to putting eyes in water when he is ready--and don't let go of him. Another fun thing at this age is dropping pool rings on the steps and let him reach down to pick them up.
final notes on safety--don't overdo the going underwater right away-and if you do, try to draw him forward so the water goes over the nose instead of up it; limit your time in pool to 20-30 min per session and make sure he is not too cold; and keep him away from pool area when not supervised (do you have a pool fence?).
Happy swimming!