Hally has learned several things during this one-act play. Some are straightforward pieces of information. For example he learns that his drunkard of a father is finally coming home from the hospital. Hally is not happy about that.
Hally also learns the reason why Sam could not stay with him in the park to fly the kite that Sam had made for Hally. Sam is a black servant, and the park area was classified as a whites-only location. In addition to learning why Sam could not stay, Hally learned the reason why Sam made the kite. It was to help take his mind off the embarrassment of having his passed-out drunk dad carried out of a bar in front of so many people.
By the end of the play, Hally has also learned to assert his authority and power over Sam and Willie. He tells Sam that Sam is nothing more than a servant and spits in his face. He also demands that Sam now call him Master Harold instead of Hally.
What Hally has not learned, though, is the damage that he has now done to the relationship between him and Sam. Sam says that if Hally wants Sam to call him Master Harold, it will be that way forever. Never again will Sam call him Hally. Sam knows that their relationship is forever changed from this point forward. Previously, Sam was sort of a father figure to Hally because Hally's real father was too drunk most of the time to be a father. Sam filled that role. Hally has not learned that because of his actions, Sam will never again be that father figure, confidant, and nurturing friend that he was previously.