If your order is more than 2500 USD you need to put the social security number, I don't know more specifically why Fedex needs it.
In France you need to pay the French customs the value added tax of the total value.
https://en.wikipedia.org/wiki/Value-added_taxIn France the VAT is 20%.
What is that for a number in Germany? Is that my normal Tax Number?
Depending on what service you used, they will contact you and ask you for the details they need.
You could also just call the call center and tell them about your order and ask what kind of documents you need to provide to speed the whole thing up.
The callcenter for the transportation services like UPS, i think you mean.