SS Obergruppenführer Felix Steiner was in command of the impressively sounding "III SS Germanisches Panzerkorps". By late April, as Soviet armies were encircling Berlin, Steiner was situated near the town of Eberswalde, about twenty-five miles northeast of the capital. This put him in an ideal spot to attack the right flank of the Soviet 1^st Belorussian Front, at least according to the situation maps in the Führerbunker.

As you see in the film, Hitler already had a loose grip on reality at this point. He believed that what he called "Army Detachment Steiner" (which would be the III SS Panzerkorps and the remains of other units in the area) could break the Russian advance and save Berlin. Hitler took inspiration from Frederick the Great: "Whoever throws his last battalion into the struggle will be the winner." Steiner received orders to attack straight from the Führerbunker late on April 21. He and his staff were threatened with execution is they failed. Compared to Hitler's delusional vision, the true situation was vastly different.

When Steiner received the attack order, he was justifiably shocked. His III SS Germanisches Panzerkorps by now consisted of barely three battalions and a few tanks. Besides this, they were exhausted, lacking supplies, and still engaged in heavy fighting. Steiner rang General Krebs to try and explain the true situation, but Krebs was practically standing next to Hitler when he took the call, and had no option but to reaffirm Steiner's order.

The famous scene in the movie is set during the midday situation meeting on April 22. All that morning Hitler had demanded to know if Steiner had gotten his counterattack underway. By now, Soviet forces had broken the outer defenses of Berlin. When he was informed that Steiner was unable to counterattack, Hitler flew into a rage. He had already accused the Army of failing him, and now the SS had failed him too. As his anger subsided into sadness, Hitler told his assembled generals that anyone who wished to leave was free to do so, but he would die in Berlin.

To sum up: Steiner's mission was nothing less that the rescue of Berlin and the salvation of Nazi Germany. Hitler was living in a fantasy world at this point, so it's hard to say whether he truly believed that Steiner could carry out the assault. In any case, it was impossible. Nothing was saving Germany at this point.

I hope this was helpful. "Downfall" is one of my favorite World War II movies.

Source: Berlin: The Downfall 1945 by Antony Beevor.

Not to discourage other responses, but /u/Aleksx000 answered almost the exact same question here