Value represents the additional cost for mounting a weapon above the value of the weapon itself. This is primarily used in character creation when building your starting vehicle.
The Space Used number represents how much of the vehicle's Space is consumed by the weapon. For example a sports car has a Space of 2 which allows you to mount a machine gun or two other firearms on the car. Flamethrowers, and missiles are too heavy for the sports car but they fit in a compact car or larger just fine.
Using crude fuel increases your vehicle's fuel consumption. This is represented by an increase in the vehicle's minimum number of tanks of fuel required per day of use. High grade fuel has the opposite effect, decreasing the minimum TPD.
That's it for part three. Stay tuned for the part four when we cover the horrific nature of...CREEP!