Abilities generally describe a creature's physical and mental characteristics, and determine the creature's strengths and weaknesses. Ability modifiers, based on the ability scores, contribute to all kinds of effects like attack rolls, defenses, and skill checks.
The ability score is the basic value of an ability, with 10 roughly representing an average for humans. The ability score is used for a few things, such as Constitution score determining a character's starting maximum hit points, but ability modifiers (see below), which are derived from the ability scores, are more commonly used.
An ability's modifier is usually the part of the ability that is used for attack rolls, defenses, skill checks and other features of your character. Ability modifiers start at +0 at an ability score of 10, and go up by 1 with every 2 points increase in the ability. You can either use the formula below to determine an ability's modifier or you can look at the table below that.
Ability modifier formula
1. Subtract 10 from the ability
2. Divide by 2
3. Round down
Example: Griff has a Strength score of 15. His Strength modifier is (15−10)/2 = 2.
Ability modifier table
|And so on...|