Lift is generated by the wing's airfoil deflecting air and creating a pressure differential. Two principles work together: Bernoulli's principle (faster-moving air over the curved upper surface produces lower static pressure) and Newton's third law (the wing deflects air downward, and the equal-and-opposite reaction pushes the wing up).
As AOA increases, the coefficient of lift (CL) increases — up to a point. The wing reaches its maximum CL at the critical angle of attack, typically around 15-20 degrees for a general-aviation airfoil. Beyond the critical AOA, airflow separates from the upper surface and the wing stalls.
The most important consequence for a pilot: a wing always stalls at the same critical angle of attack, regardless of airspeed, weight, bank angle, or attitude. You can stall at any airspeed and any attitude if you exceed the critical AOA. This is why stall awareness is built around AOA, not just the airspeed indicator.
The thin layer of air in contact with the wing is the boundary layer. At low AOA it stays attached and flows smoothly. As AOA increases toward critical, the boundary layer thickens and eventually separates, creating turbulent, low-energy air that destroys lift and increases drag — the stall.