Lynn has a point.....am I the only airline pilot who gives a running commentary of what I'm doing over the PA?
If you do it in the United States below 10,000 feet or while in movement on the ground, you are in violation of 14 CFR 121.542 (for airlines). Explaining how the airplane works or other pedagogic announcements are not essential to the safety of the flight and are therefore prohibited. Your job is to fly the aircraft, not to make presentations to passengers.
A number of recent accidents have been linked in part to non-essential conversation in the cockpit, so this is not a good time to test the leniency of the FAA.