Since races and specializations vary, I reserve the right to add modifiers as I see fit. You can argue, however, if you find them unfair.
You need at least 40 points for a stat for it to not have a negative modifier (-1 for each 10 points lower than 40)
Beyond 40, each 10 stat points will add a +1 modifier to your rolls. Sometimes if the situation is more delicate, I might use a d12, and the rule for the results will be like the d6 one, with some more gray areas.
Strength determine actions that require athletic powers, like bending iron bars, running in one direction, and anything involving using your physical might.
Finesse determine actions that involve precisions, like lockpicking, aiming projectile weapons, parkour, and trying to stab somebody in their vital spot.
Mindpower determine basically all mental work that doesn't require finesse, really. From resisting the overwhelming mind control of a deity, to just trying to understand a difficult book.
Luck determine an action that require things beyond your actions, like having a guard chasing you trip on a stone while you are running. Et cetera.
Aptitude is not really a roll modifier, but it affect your stat growth.
Experience, Specialization and Aptitude
Every 20 time you fail at certain actions using a certain stat, you will get one stat for them. This exclude Luck, in which you can only get from Blessings.
Specialization is a special modifier type you can choose for a narrower type of skills. You will have to sacrifice 10 stat points from the Stat governing that skill for them. Specializations will give you a +1 modifier on action using them. For instance, if you spend 10 Intelligence points in Bugs Chemical Extermination, you will get a +1 modifier when you try to spray a cockroach with pesticide.
As said earlier, Aptitude is a special stat. It does not help you directly in rolls, but it can speed up your experience growth slightly. You get 1 more Aptitude point after getting 10 Epic Success Rolls. When one of your stat or specialization go up, I roll a %d. If the result is lower than your Aptitude point, you will get an extra stat (or specialization). You stop getting Aptitude points when you reach 100.