Bernoulli's Principle
Bernoulli's Principle: an increase in the speed of a fluid produces a decrease in pressure and a decrease in speed produces an increase in pressure.
Sounds complicated! Watch the video below to get a better idea of Bernoulli's principle.
And check out the graphic and caption below...
The curved top of a wing creates a longer distance from front to back than the straight bottom. This causes the air on top to travel farther, and thus faster, to reach the back than the air underneath, creating a difference in pressure between the two surfaces