The nexxOMNIA API can be complicated to handle, as there are Tons of Options and Modifiers everywhere. Nevertheless, the Structure is always identical and the Parameter Options are always covering the same Concepts, once they are used.
Make yourself familiar with the general Structure and Authorization
The most common Parameters and Modifiers, valid for all Parts of the API, are explained here
It is impossible to layout a valid Response Object even within a single API. That is due to the Concept of Output Modifiers and List/Single Item Types. Therefore, only the basic Response Object Attributes can be described here