"- or negative" in laymans terms means this. lets say you move the aileron stick to the right. With nothing on, the aileron moves right along with the movement of your stick.
* Now with lets say -25%, you move the stick to the right but the aileron is lagging behind thus feeling a bit sloppy. The more -% you dial in the more sloppy it gets. It is a bit more relaxing to fly this way.
* If you go to the "positive side" your really asking for trouble as you barely breath on those control sticks and the plane is going to do things that will mess your pants.