Core rule
Ability scores and modifiers
Ability scores describe a character’s strengths. Most rolls add the ability modifier, rather than the score itself.
The six abilities are Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma. Scores of 14 and 15 give +2; 16 and 17 give +3.
Without other effects, reaching the next even score increases the modifier by one. Raising 15 to 16 therefore improves rolls using that ability.