The Strength score determines item slots. Its modifier affects melee & thrown damage. Its Tests concern strength.
The Dexterity modifier affects Move & Stealth, and Defense if no armor is worn. Its Tests concern nimbleness and coordination.
The Constitution score (& the PC's level) determines hit points. Its modifier will often affect Saves concerning disease. It involves tests regarding endurance.
Intelligence is helpful for solving difficult problems and its modifier determines known languages. Knowable languages = 1 (native) + Int. Its Tests concern knowledge and intellect.
~~Wisdom~~ Perception is used for initiative and can be used for detecting lies and perceiving.
Charisma can be the RP easy button and modifies Reaction rolls. Unlike in other GLOG rules, Charisma isn't tied to your Save. Its modifier determines your max number of henchmen/retainers, calculated as: 2 + Cha.