At the conclusion of the play, Biff has learned, or at least finally acknowledged, the truth about his own life and his father's life. He tells his father that they are both "a dime a dozen" and that neither of them is "a leader of men." Biff recognizes that some kind of decent life is waiting for him "the minute I say I know who I am!"
Biff also understands how destructive his father's lifetime of denial has been for both of them. "I'm nothing! I'm nothing, Pop . . . . Will you let me go, for Christ's sake? Will you take that phony dream and burn it before something happens?" Biff's words are quite true and foreshadow Willy's suicide at the play's conclusion.
I'm not sure he learns anything because what he states at the end of the play is something that he knew for a long time. He does seem to learn something when he utters the famous line, "I'm nothing! I'm nothing, Pop . . . . Will you let me go, for Christ's sake?" But the fact is that he isn't "nothing." Saying that he's nothing will not get rid of the fact that he is something, even if that something isn't what his Dad pumped him full of.
I think he would have learned something if he had come to understand and forgive his father for his failings, if he had learned that his father and he were both something and they both had their human dignity. If Biff could have forgiven his father, if he had learned that forgivness is an essential element to happiness, Willie might have lived. Of course this could not have happened in that final scene of the play, and it's understandable that he reacted as he did when he found his father. But his anger damanged both his life and his father's, and it was all probably avoidable.
I know that many people don't see the play this way, but I think it's a valid reading and in keeping with Miller's vision of human dignity and the complexity of situations we find ourselves in.