Immediately before takeoff, flight attendants typically remind passengers to fasten their seat belts and prepare for takeoff. However, the procedures vary depending on the airline. In addition to this statement, there is a long list of things covered before a plane takes off. A flight attendant usually conducts a demonstration that covers this information.
It's estimated that there are around 5,000 planes in the air over the United States at any given time. There are probably a couple of thousand more airplanes flying in other parts of the world, and about 500,000 people are in those planes.