Zack,
This stuff has been covered too many times. Please use the "Google search the board"
function at the upper right of the page for a more in depth explanation, since what
I'm going to tell you is just the quick and dirty.
The wind doesn't hit the face of the blade perpendicularly, it hits it at an angle
because the blade has what is known as "pitch". This serves to make the leading edge
of the blade encounter the wind a millisecond or two before the trailing edge does.
The side of the blade facing the wind is flat, the other side has an airfoil
shape. When wind hits the blade it's split between the two sides, causing a high
pressure on windward side and a low pressure on the leeward side. High pressure
air (forward flat side) is deflected by blade angle (pitch) towards the trailing
edge. Low pressure air (back curved side) must speed up (it has slightly farther to
go) to catch up with with its brother air molecules that it was so rudely separated
from by the leading edge. This "stretching" causes the low pressure or "lift" on the
curved side of the blade. Since the blade has pitch, that low pressure air (think
suction) is imparting a bit of force on the blade, inducing it to move in the
direction closest to the low pressure that it can, as limited by the turbines shaft.
The flat (forward facing) side of the blade contributes to the rotation also by
imparting (due to pitch) a direction change in the local air mass which causes a
deflection pressure against the face of the blade, which again is moderated by
the turbines shaft.
As far as wind coming from the side... Uh-uh, think about it, the forces would
cancel each other out.
Read, then read more, -Gus