This is my first time playing a warlock and I'm still fairly new to tabletop games, so I could use guidance. I know that eldritch blast does 1d10 force damage, and by 17th level, it has four beams when cast.
The PHB description for the Agonizing Blast eldritch invocation (PHB, p. 110) says:
When you cast eldritch blast, add your Charisma modifier to the damage it deals on a hit.
I've looked around and many different areas say add ability score, some people say add modifier, so its all different things.
Let's say my Charisma score is 15 (a modifier of +2). When I roll to do damage for eldritch blast, am I adding 1d10 + 15 (i.e. my Charisma score), or 1d10 + 2 (my Charisma modifier)?
Best Answer
Add the modifier (+2)
As you say, agonizing blast allows one to "add your Charisma modifier to the damage [*eldritch blast] deals on a hit." (PHB p.110, emphasis mine)
Your Charisma modifier is +2, as you can see from PHB p.13. (Or many of us end up memorizing the mathematical rule: "subtract ten, divide by two, round down" to get from score to modifier.)
As a side note: almost everything in the game is going to reference your ability modifier rather than your ability score. Jump distance and movement speed in the Astral Plane are the two exceptions I can think of off the top of my head. Multiclass prerequisites and push/pull/drag capacity for those who track weight, armor prerequisites... a few other things? Point being, they're few and far between.