A command, an order, an Auftrag are all forms in which military commanders communicate their intent. They are different in character, however. Commands and orders are strict, well defined, to be executed as stated. An Auftrag is the least strict in the sense of prescriptive, of defining the how as well as the what.
A command or order allows for little freedom in defining the how. A command defines the what and the how in detail. An Auftrag describes only the goal, thus allowing freedom to choose the best path to it. An Auftrag communicates intent, clearly and within the broader strategic context.
Depending on the situation, the line between an order and an Auftrag is in flux. The core of an Auftrag is the what. It can, though, include parameters such as the when and the where. The more detailed an Auftrag is about the how, the more it takes on the character of a command or order.