Why does the air flow more quickly over the top of the of the aerofoil? To understand why this happens you are going to have to look at what happens in the first moments as the air begins to move around the aerofoil. You are also going to have to think of moving air as behaving like a fluid. It might be a good idea to fit in a fluid dynamics course at this point, but as an alternative you can try a simple experiment.
Position a flat (low-camber) soup spoon in a tray of salted water as in the diagram, and use a thin stick to place a drop of food colouring on its trailing edge. Turn the spoon to a low angle of attack, move it quickly to the left, and you should now see a starting vortex rotating in an anti-clockwise direction.
It is difficult to think of of air as having a viscosity or 'thickness', but moving air does and this internal friction changes the way that it moves past surface edges, such as the sharp trailing edge of the aerofoil.
The air initially moves above and below the aerofoil at the same speed, but the air below the aerofoil reaches the training edge first and momentarily flows around the trailing edge.
Fluid flow around such a thin shape is unstable (you are just going to have to accept this until you take the fluid dynamics course), and a starting vortex develops at the trailing edge of the aerofoil.
The energy required to create the starting vortex has the effect of 'pulling' on the air flow over the top of the aerofoil, increasing its speed. The flow over the top continues to move faster than the air flow below the aerofoil whilst it remains in motion.
As the aerofoil moves forward it sheds (leaves behind) the starting vortex.
In the early 1900's, theoretical developments allowed this process to be described mathematically for the first time in the circulation theory of lift. Aerodynamic experiments by Ludwig Prandtl then led to the simple curved wing profiles used by the early innovators giving way to the thick aeofoil, made famous by the Foker Triplane of 1917. This form of aerofoil dramatically improved the performance of planes. and led directly to the development of the modern day aerofoil.
Wing profile used by Lilienthal, the starting point for the Wright Brothers.
Göttingen wing profile of the famous Fokker Triplane of 1917.
Fokker Triplane

Learn how planes really fly with the new 'How Planes Fly' section.

Learn how planes really fly with the new 'How Planes Fly' section.