I am managing to receive a fixed structured table from a questionnaire in a web form.
So I want to have this table automatically forwarded to a specific spreadsheet, so that I can make my own statistics in the collected data.
That is not possible. It will take extensive coding to make that happen.
You should have considered using Google Forms in combination with Google Spreadsheets. Google Forms is perfectly equipped to function as a questionnaire. It can be embedded on a website, Gmail or used live (own URL).
In Google Spreadsheets, all data is gathered, no matter where the entry has been made. Here you will able to make all necessary calculations !!
See help page Google Drive: Google Forms