How do airplanes actually stay in the air?

Lift comes from the wing pushing air down. As a wing moves through air at a slight upward angle, it deflects the airflow downward, and by Newton's third law the air pushes the wing up with an equal and opposite force. That downwash is measurable behind any aircraft, and it is the honest core of the explanation. The pressure description is also valid and describes the same physics from another angle: airflow over the curved upper surface is faster and at lower pressure than beneath, and the pressure difference across the wing produces the upward force. Both descriptions are correct because they are two accountings of one phenomenon.

What is wrong is the common textbook add-on, the equal transit time theory, which claims air separating at the leading edge must meet again at the trailing edge, forcing the top flow to travel faster. There is no such requirement, and measurements show the upper flow arrives well ahead. That flawed explanation also fails to explain why planes fly inverted, why flat wings generate lift, and why angle of attack matters so much. The practical variables are angle of attack, airspeed, wing area, and air density, which is why planes need long takeoff rolls, why flaps extend for slow landings, and why high-altitude airports demand longer runways. Push the angle of attack too far and the flow separates from the wing, lift collapses, and the aircraft stalls, which is not an engine failure but an aerodynamic one.