If surface Normal is a Vector that Perpendicular to Surface, Why we specified surface normal by only one point. ( I mean by one glNormal3f(,,,); per vertex. ) Where''s another one? (You need al least two points to create a vector, right?) and In redbook they specified normal to every vertex. But NeHe tutorial specified only one per face. What the difference between this two? Thanks a lot.

A vector consists of direction and magnitude. A triple of coordinates is all that is necessary to indicate those values in three space. If it makes you feel better imagine that the vector is the vector specified from 0,0,0 to the coordinates of the vector.
Specifying a normal for every vertex allows things such as goraud shading and other gradual shading methods.