::Yes correct – the chance to hit (using the d20), not the actual damage itself.
Once the attack roll succeeds (i.e. rolls higher than the opponents AC), the next roll comes into play, being the Damage Roll.
The damage roll generally consists of rolling a specific type of die (or dice) as indicated by the weapon or spell being used. This is usually like a d8 (8 sided dice).
The formula for a basic damage roll is: Damage = Dice Roll + Ability Modifier + Other Modifiers.
For example, the fighter hitting the goblin using something like a longsword will need to roll a d8 after the d20 roll succeeds to dictate how much damage will be applied to the Goblin’s Hit Points (HP).
For melee weapons, the Strength modifier is usually added to the damage, and for ranged weapons, the Dexterity modifier is typically used. (Note that some class features or feats might allow a character to use different ability modifiers for damage rolls, or add additional bonuses).
So in this case, the Fighter’s Ability Modifier (being +3 Strength) is also applied during the Damage Roll (in the same way as the Attack Roll with the d20). So if he were to roll a 6 using the d8 roll, he would do:
Other Modifiers: Some classes and feats allow characters to add additional modifiers to damage rolls, or use alternative ability modifiers. For instance, a Rogue’s Sneak Attack feature allows for extra damage, and the Finesse property on some weapons allows the user to choose between using Strength or Dexterity (whichever is the highest) for both attack and damage rolls.