“competent, skillful, clever at or in a certain action” –
be good at (something/ doing something) – areas of expertise
Nadal is good at tennis.
He´s good at playing tennis. (PREPOSITION + VERB-ING)
Einstein was good at physics.
be good with – talking about people or specific things
Are you good with numbers?
He is good with computers – He is good at using computers
She is good with children – She is good at dealing with children.