[klausb]

1:
now I can set one boundary condition but when I "LMB-click into the 3d view...", I end up with a red box (see attachment).

2:
When I continue to create boundary conditions, only the last one created is stored (I checked it using "view > boundary codes" or "simulation > edit boundary conditions")

3:
How can I get hold of the faces of the damper to set the boundary conditions?

[ogloth]

Are you by any chance using the "select all visible" option. That would sett all visible faces to the same boundary code.

[klausb]

... I came to the point to create the new volume.

I added vol but can't select "green" in the new column, the available options are "A <<" and ">> B".

I continued with the default setting "A <<" (whatever that means) and created the mesh as described in the tutorial.

Klaus

[ogloth]

see this thread:
Surface orientations