How and where do I enroll as a student?
To enroll, foreign students can register online at the Georg-August-University Göttingen and submit their documents before the semester begin. 
Even though you registered online at the Faculty of Agricultural Sciences in Göttingen to apply for admission you have to register online again at the University in Göttingen to enroll.  
International Students enroll and submit their documents to: 
Göttingen International 
von Siebold Str. 2
37075 Göttingen 
German students enroll and submit their documents at 
Studienzentrale 
Wilhelmsplatz 4
37073 Göttingen
New students may also choose to wait and enroll upon arrival in Göttingen. The process might take up to two weeks. Similar to the admission process the enrollment involves several steps.
Find more information in the following link. 
http://www.uni-goettingen.de/en/46858.html