A character’s Dexterity is a measurement of their coordination, speed, and grace. Dexterous characters have faster reflexes, more nimble movements, and better balance than other people.
Your Dexterity score applies in the following situations:
In situations where your character needs to move nimbly, quickly, or quietly or to keep from falling on tricky footing, or to perform physical tasks focused on deft-fingered movements rather than force.
Some examples of Dexterity checks include:
Dexterity is the default ability when making some melee Attacks and most ranged weapon Attacks. When you make an attack roll using a ranged weapon like a crossbow, longbow, or sling, you add your Dexterity modifier to the attack roll and the damage roll. When using a melee weapon with the Finesse property (such as a rapier or whip), you can choose to use your Dexterity modifier instead of your Strength modifier.
Some classes, like The Monk, also have the ability to substitute their Dexterity modifier for their Strength modifier when making unarmed attacks.
Depending on the armor you wear, you might add some or all of your Dexterity modifier to your Armor Class. Characters wearing light armor or no armor at all, for example, add their Dexterity modifiers to their base AC.
Typically, at the beginning of each combat or turn based sequence, all participants “roll initiative”, with the most common modifier to the roll being Dexterity. This determines the order in which the combatants act.