http://cromagnon.stanford.edu/~sturd.../liftsuck.html

http://www.aa.washington.edu/faculty/eberhardt/lift.htm

http://www.turnertoys.com/G1/aeroScience/default.htm

are three good sites to read respect to lift of wings. To do it properly you must do, as Ken said, the math. But the bottom line is,

That it is not really impact on the bottom of the airfoil or flat plate.

That anything at angle of attack undergoes what is called "circulation" and in the process there is a lower pressure generated on the top and a higher pressure on the bottom.

That pressure differential produces the "lift" that the wing feels.

The process of generating lift makes downwash behind the wing, the magnitude of which is representative of the lift being generated.

Some folks think that the downwash flow reaction is what generates lift. It is not. It is a result, not a cause of lift.

It is not a simple easily described subject based on the fact that there are a whole lot of text books written on the subject. There is also a lot of misinformation about it resulting from bad science presented as fact for years.