Attack:
Increase your attack rate and your piercing rate. Your attack rate is the damage dealed by your weapons, adding this stats will give you extra damage on your weapons. Piercing rate is really similar to the above but instead of increasing your weapon's damage, it is decreasing your enemy's defense.
Fuel:
Increase your maximum fuel volume and your maximum weight. If you run out of fuel, you die. The maximum weight is also important, below 70% there are no effects. If you are within 70%-80%, you will lose twice as much fuel. If you are over 80%, your booster will also be disabled.
Agility:
Increase your evasion ratio, this is useful to evade attacks. It will not reduce the time between two rolls.
Defense:
Increase your defense ratio.
Spirit:
Increase your maximum skill points(SP). Skill points are used with skills, depending on the skills you have, more SP would allow you to use more skills in a fight.
Shield:
Increase your shield quantity, this allow you to take more damage before your enemy starts to hurt your energy. If you have 0 energy, you die. If you have 0 shield and 1 energy, you are alive.
Source: Space Cowboys Fans
