What is the purpose of the P gear in an automatic transmission?

[StDonovan]

Automatic transmission P gear is the parking gear and starting gear. When the vehicle is parked and not in use, shifting into P gear engages a mechanical lock on the wheels to prevent rolling. The P gear utilizes a mechanical device to lock the rotating parts of the vehicle, preventing movement. When a vehicle needs to remain stationary for an extended period or before leaving the vehicle after parking, the parking brake should be engaged and the gear selector moved to the "P" position. An automatic transmission eliminates the need for the driver to manually shift gears, as the vehicle automatically selects the appropriate gear based on driving speed and traffic conditions. Typically, automatic transmission vehicles have six gear positions arranged from top to bottom: P, R, N, D, S, L.