The difficulty here is not that the two philosophers disagreed. It is that we have no direct access to one of them. Socrates wrote nothing, and every account we possess was written by someone with an agenda: Plato, who revered him and used him as a mouthpiece; Xenophon, who portrays a more conventional moralist; and Aristophanes, who made him a comic figure in a play. Scholars call this the Socratic problem, and it has no clean solution.
The working convention is developmental. Plato's dialogues are grouped into early, middle and late, and the early ones share a distinctive shape: short, focused on defining a single virtue, driven by Socrates questioning someone confident, and ending without a definition anyone can defend. That shape is so unlike a philosopher presenting his own views that it is generally taken to reflect the historical Socrates' actual practice.
The method itself is the elenchus. Socrates asks someone to define a term they use confidently — courage, piety, justice. He then draws out consequences of the definition until it conflicts with something else the person firmly believes. The definition is revised, and the process repeats. Frequently the dialogue ends in aporia: acknowledged perplexity, with the participants no longer able to say what they thought they knew. That is presented not as failure but as progress, since recognising ignorance is the precondition for enquiry.
The middle dialogues change character completely. Socrates now speaks at length, and what he delivers is a system: the theory of Forms, the tripartite soul, the immortality of the soul, and in the Republic an entire ideal state governed by philosopher-rulers. The interlocutors mostly agree at intervals rather than genuinely resisting. Few scholars believe the historical Socrates held these doctrines — Aristotle, who studied under Plato, indicates that the theory of Forms was Plato's addition — and the character has become a vehicle.
So the honest summary is this: Socrates contributed a method and a stance — persistent questioning, intellectual humility, the conviction that the unexamined life is not worth living and that virtue is bound up with knowledge. Plato contributed the system, the metaphysics, the political theory, and the literary form that carried all of it. Trying to draw the line more precisely than that is where the scholarship becomes genuinely contested, and anyone claiming certainty about which specific views belong to which man is claiming more than the evidence allows.