Hi Chris,

thanks a lot.
Now it is working.
I am happy/ich bin glücklich.

So at least I have a VM and installed Tails.

Problems occured in using Tails.
I wanted to play around to get a full screen e.g. and my laptop stopped 
after using the key contr + L and contr + S (this was suggested by Tails 
to get the mouse running, because the mouse was not working any more)
I had to start my laptop again.
But that's another problem, it isn't a Guix question.
I have to find out answers somewhere else
or
if a Guixer is using Tails in a VM, he could help me to set everything up.

Gottfried