well im not german but i'll try to explain.
the thing you have to add the command line to is the steam shortcut on your desktop. if you dont have one, then make one
if you go to the steam folder just right click on the steam icon and make a shortcut to desktop, then rightclick on the desktop icon, and there you should add the commandline.
in the end it should look like this:
"C:\Program Files\Steam\Steam.exe" -clientbeta newfs -beta fs
maybe it would be good if steam was shut off while you do this. then start steam, log in, and steam will update itself. when it is logged in, steam will check red orchestra for completeness, whatever it is called again
it will automatically create the new map. you dont have to copy this yourself.
when this is done, just launch red orchestra from steam ( wich you now have to start up from the desktop i presume, dont know about that )
hope this is helpfull to you