It's in the game manual.
# Handling: Allows the player to avoid losing the ball to the opposing defense while dribbling. Important against a pressing defense (to be added later) or, in general, against good perimeter defense. Teams with good handling will have more success at creating quality shot opportunities.
# Passing: Helps to create good shots (and get assists). Bad passing can also lead to turnovers.
And passing increases a player's salary more than handling.