dexterity (uncount): skill in using your hands or your mind
You need good manual dexterity to be a dentist.
skillful (adj): (of a person) good at doing something, especially something that needs a particular ability or special training
a skillful player/performer/teacher
Ok, say you and your child were playing a game of stacking toys.
He tried but didn't succeed. The stack fell off every time he tried.
Do we say "you need good manual dexterity" or "you need to be skillful"?