At the higher level, two regiments formed a brigade. Two brigades (along with an artillery brigade, a cavalry regiment, two medical companies and two engineering companies) formed a division.
During the invasion of the Belgium and the Battle of the Marne, Walter is in:
IV Reserve Corps
22nd Reserve Division
82nd Reserve Infantry Regiment
As the army suffered casualties, lower ranking officers often came to command larger units. In particular, the Imperial German Army was slow to promote non-commissioned officers to commissioned ranks (say, a sergeant or gefreiter to leutnant) and so an NCO might end up leading a Zug or perhaps even for a brief time a kompanie.
The structures shown here changed as the war went on, as the nature of the war came increasingly to demand small group tactics and more heavily armed men with different specialties. However, at the beginning of the war, the vast majority of soldiers were riflemen and infantry companies were made up almost exclusively of riflemen.