Wing incidence is the angle of the wing in relation to the datum line of the plane (line that runs lengthwise throught the center of the plane plane).

When you have a 0 incidence, the wing is at the same angle as the datum line. It neither helps lift the plane or pushes it down.

When you have a plus incidence, the leading edge of the wing is higher than the datum line. This means the wing is at an angle. As the air flows over the wing, the wing is going to want to lift faster than just the airfoil alone would allow. The plus side is that SOME planes need a positive incidence (more lift per se) in order to fly properly. The downside is that if you have too much incidence, the plane is going to take off before the plane is moving fast enough to actually fly. The plane is going to tip stall and (usually) crash.

The incidence on the horizontal stab is USUALLY set at 0. There are some cases though where you may want to adjust it to alter/fine tune the flying characteristics of the plane.

I suggest setting the incidence as called for in the manual, and then AFTER FLYING THE PLANE decide if you want to alter them. If you do decide to alter them, USUALLY the main wing is the only one that is adjusted. I would suggest not making any changes greater than 1/4 - 1/2 degree at a time. If the incidence is not specified in the manual, I suggest setting the the incidence at 0 degrees on the main wing and 0 degrees on the horizontal stab.

Hope this helps.