The only resource that explains anything about that buffer structure is the book "Practical Rendering and Computation with Direct3D 11".
There it is something like:
Each of these numbers represent a 4 byte size:
0 = Alligned Byte Offset For Args (uint) 1 = Alligned Byte Offset For Args (uint) 2 = Alligned Byte Offset For Args (uint) 3 = Vertex Count Per Instance (uint) 4 = Instance Count (uint) 5 = Start Vertex Location (uint) 6 = Start Instance Location (uint)
0-2: Is space available for whatever data I want? Can this be expanded arbitrary? Is this the number of bytes I have to skip and can be used in DrawInstancedIndirect as second parameter (AlignedByteOffsetForArgs)?
3: This must be 1 for me since I am drawing 1 vertex per particle and will create a billboard in the geometry shader.
4: I guess this is the actual number of particles that are drawn.
5, 6: Well no idea about these two.