Most foreign students need a valid visa for entering Germany. Detailed information about the regulations can be found at the Deutscher Akademischer Austauschdienst (DAAD) on the page Entry and residence.

Immediately after arriving in Hanover you must apply for a residence permit. The DAAD has worked out a detailed information sheet answering all questions concerning visa and right of residence: Information on the Statutory Frameworks applicable to Entry and Residence by Foreign Students, Academics and Researchers [PDF].