Short answers, pulled from the story.
The Territory of the Military Commander in Serbia was a German-occupied region of the Kingdom of Yugoslavia during World War II, including the Banat and the northern part of Kosovo. It was governed nominally by a Serb puppet government under Nazi control and was the only part of occupied Yugoslavia where the Germans set up a military government outright.
The Territory was established in April 1941, after the German Wehrmacht and other Axis powers invaded and partitioned the Kingdom of Yugoslavia. On the 22nd of April 1941, it was placed under the supreme authority of the German Military Commander in Serbia.
Milan Aćimović led the first puppet administration, the Commissioner Government, formed on the 30th of May 1941. General Milan Nedić led the second, the Government of National Salvation, formed on the 29th of August 1941 after the Commissioner Government failed to contain a growing uprising.
German forces, aided by Serbian collaborators, murdered nearly all Jews living in the Territory. The killings came in two waves: mass shootings of men in 1941, followed by the gassing of women and children in mobile gas vans in early 1942.
The Territory dissolved in 1944, when the Germans withdrew in the face of the Belgrade Offensive carried out by the Red Army, Bulgarian forces and the Yugoslav Partisans. The German administration evacuated to Vienna that October, and Nedić's Government of National Salvation dissolved with it.
Germany ran it as a direct military government because the region held key rail lines, Danube transport routes and valuable non-ferrous metal deposits. It was the only part of occupied Yugoslavia where German occupiers ran this kind of direct rule, rather than delegating to a puppet state with formal standing.