How does mapping work?

Perhaps I’m too dense.

Let’s try this:
New model mm
Create a planar srf 100x100
Open Materials panel
Import ‘Abachi poliert’
Drag&drop the material to the srf
Set Rendered view

Ok so far.
Now let’s try to edit the mapping.
As a first thing, I want to rotate the material 90°.
In the Properties panel, I select mapping.
I get this:

I can enter values everywhere.
But it never changes something!

Several possibilities:

  • I miss something important
  • The system doesn’t work
  • I don’t understand the system at all

So what are the correct steps to edit the mapping?

It’s probably because the texture mapping on the material is set to WCS instead of “Mapping Channel”

And how to change that?

Edit:
Found.

Edit 2:
Why is there no message that the mapping won’t work?

Rem.:
The material/mapping UI is far too complicated.
There is too much knowledge needed to handle such simple things like just rotating a texture.

The very first experience is: Doesn’t work.