The citation was taken from “How to import.txt” and since it was not understandable for me, I wrote my question.

I have now completed my theme install and was confused – the assignments was allready done automaticly! The cited sentense should therefore be deleted in the instruction.

In return, important information is missing, namely that the Contact Form plugin MUST be installed before importing the “therestaurant.wordpress.2013-03-25.xml”!