How is lift created?

In my uni years I went to a lot of science conferences; one of the papers that I remember very was about ships propellers and how it can create thrust. A comparison was made with lift on an aerofoil. As the author put it, the lift appears as a pressure difference on the tow faces of the aerofoil. The difference appears because the velocity of air on the upper is larger than that on the lower face. And finally, this velocity difference is because of the upper edge of the aerofoil section is larger and the particles would have to travel faster in a given time.

This is wrong.

First of all lets clarify some ideas:
1. Lift is a force, and in fluid dynamics forces are the results of pressure differential.
2. The concept that the bigger the velocity, the lower the pressure is based on Bernoulli's equation (conservation of energy), but this can be applied only on the same streamline (see post on lines in FD).
3. There is no law or experiment that states that the particles that split at the leading edge must combine at the trailing edge at the same time; actually there is evidence that in order to create lift, the particles on the upper surface reach the trailing edge before those on the lower surface.

The correct explanation is the following.
The shape of the aerofoil creates pressure gradients; for a curved streamline, the pressure will be higher on the convex side. This pressure differential accounts for the force; from the force and pressure the velocity is derived.

From this the conclusion is that aerofoil profile is the most important for the lift; a straight profile can't create lift.