HOW THE AUTOMATIC TRANSMISSION WORKS

  The transmission is a device that is connected to the back of the engine and sends the power from the engine
  to the drive wheels. An automobile engine runs at its best at a certain RPM (Revolutions Per Minute) range
  and it is the transmission's job to make sure that the power is delivered to the wheels while keeping the
  engine within that range. It does this through various gear combinations. In first gear, the engine turns much
  faster in relation to the drive wheels, while in high gear the engine is loafing even though the car may be
  going in excess of 70 MPH.

  In addition to the various forward gears, a transmission also has a neutral position which disconnects the
  engine from the drive wheels, and reverse, which causes the drive wheels to turn in the opposite direction
  allowing you to back up. Finally, there is the Park position. In this position, a latch mechanism (not unlike
  a deadbolt lock on a door) is inserted into a slot in the output shaft to lock the drive wheels and keep them
  from turning, thereby preventing the vehicle from rolling.