Here is an excerpt from EGS about how ability score ranks work:
The Echelon Gaming System inherits the six prime abilities from the 3.5 d20 SRD. These abilities are Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma. Expansions to EGS may bring additional abilities to the game, but for now we stick the basics.
Each Ability, after changes made because of race, has a rank ranging from –5 to +∞ (infinity). Table: Ability Ranks shows the modifier for each score. Each Ability partially describes your character and affects some of his or her Actions.
The rank is the number you apply to the die roll when your character tries to do something related to that Ability. You also use the rank with some numbers that aren’t die rolls. A positive rank is called a bonus, and a negative rank is called a penalty.
The ability that governs Powers depends on the individual entry: Intelligence can be used for specific styles of Wizarding; Wisdom for divine inspired gifts; or Charisma for certain sorceries. A high rank in an Ability is the prerequisite of the most impressive Powers.
Strength measures your character’s muscle and physical power. This ability is especially important for Close Combat and Might Powers because it helps characters utilizing those powers reach their fullest potential. Strength also limits the amount of equipment your character can carry.
- Melee attack rolls.
- Damage rolls when using a melee weapon or a thrown weapon (including a sling). (Exceptions: Off-hand attacks receive only one-half the character’s Strength rank, while two-handed attacks receive one and a half times the Strength rank. A Strength penalty, but not a bonus, applies to attacks made with a bow that is not a composite bow.)
- Athletics and Intimidate checks. These are the Skills that have Strength as their key Ability.
- Strength checks (for breaking down doors and the like).
- Fortitude Saving Throws. The higher of your Strength or Constitution ranks are applied to resisting poison and similar threats.