The second question is understandable, and I think the German General was von Paulus, but I'm not really sure about the first one. Did you mean, what was their objective by capturing Stalingrad? Open road to the Caucasus, and it's oil depots.
Wiki says the commanders were Franz Halder, Wilhelm Ritter von Leeb, Fedor von Bock, Gerd von Rundstedt, Ion Antonescu (Romania) and Carl Gustaf Emil Mannerheim (Finland).
And the army group was most likely the Wehrmacht?