If you have just arrived in Bremen or Bremerhaven, you should take care of the city registration as soon as possible.
In Germany there is a registration obligation for all persons who move into an apartment. Within one week of entering or moving in, you must register yourself and all family members who have also entered the country at a citizens' registration office in the state of Bremen.

Residence Registration Office

Upon moving to Germany and getting a residential address, you are required by law to register with the local authorities within the first week. The registration is done at the Residents' Registration Office (Einwohnermeldeamt) serving your area. You will need this filled out accommodation confirmation for this purpose.

If you move and change your address during your stay in Germany, you will need to notify the Residents' Registration Office of your new place of residence in Germany. Before you leave the country, you will have to inform them of your departure at least two weeks in advance. Please keep in mind that these offices serve a large number of people daily which may lead to long waiting times.