How lasers work - a thorough explanation(best revision video) for full Laser Concept

What did I learn or Understand After Watching this video?

Meta stable state is 1000 times more stable than normal 2 Level State.

White light or Colourful photon to stimulate to 3rd energy level.

Monochromatic Amplified Collimated Beam - Radiation.

photon is absorbed only if photon energy level is equal to difference in energy levels.