You must register at the town hall where you live (Anmeldebescheinigung
/Einwohnermeldeamt) :
You must go to the town hall and ask for a registry
form. Go with your passport and your tenant contract.
The price is about 5€ and it is mandatory.
Depending on the land, this registration must occur
within 7 or 14 days after you arrive.
The German Post :
die Deutche Post
http://www.deutschepost.de
Customer services : 01802 33 (Mon-Fri 7h00-20h00, Sat
8h00-14h00)
Carry out your change of address at the Post.