Strength measures muscle and physical power. This ability is important for those who engage in hand-to-hand (or “melee”) combat, such as fighters, monks, paladins, and some rangers. Strength also sets the maximum amount of weight your character can carry.
A character with a Strength score of 0 is too weak to move in any way and is Helpless (but not unconscious).
Some creatures do not possess a Strength score and have no modifier at all to Strength-based skills or checks.