Whee... here goes... my newbie impression of wing incidence is basically the angle of the wing relative to the line of thrust of the aircraft. Raising the leading edge of the wing (relative to the trailing edge) increases incidence, and lowering it decreases incidence. This is all fine and dandy for a symmetrical airfoil, but things get complicated with a flat-bottomed trainer type airfoil... if the bottom of the wing is flat (i.e. parallel to the line of thrust) you have a bit of positive incidence, since the "center" of the leading edge will be above the "center" of the trailing edge.

I'll leave it to the experts to correct my description, and tell you why you might want (or not want) positive incidence on your wing.

-Rick (fellow newbie)