In Germany, every resident staying for more than three months must register his/her residency with the local authorities usually at the nearest town hall (Einwohnermeldeamt or Bürgeramt).
When: within two weeks after arrival, even if you are living in temporary accommodations, and within two weeks after each move.
Registration Certificate: You must save your Registration Certificate (Anmeldebestätigung) for your entire stay in Berlin.You will need to present it every time you go to the Berlin Foreigners Registration Office (Ausländerbehörde) and for many daily activities such as opening a bank account.
You can ask your landlord which registration office is near your apartment.
Please note: In the application form, you will be asked about your church affiliation. If you state one, German church tax, which amounts to eight or nine percent of your payable income tax, will automatically be deducted.