The registration office of the city or municipality where you are registered with your main residence will issue you with a written or electronic registration certificate upon request.
This requires you to provide your surname, first name, date of birth and the address of your current main or sole residence.
A registration certificate serves as proof of residence and contains at least the following data specified in § 18 Para. 1 BMG:

Surname, first names with identification of the common first name , doctor's degree, date of birth, current addresses, marked according to main and secondary residence.

On request, this data can be supplemented by the data specified in § 18 Para. 2 BMG and thus an extended registration certificate can be issued. In the event that you are unable to visit the registration office yourself or otherwise contact them, they may only hand over the registration certificate on presentation of a power of attorney or it will be sent to you by post or electronically.

It is required, for example, in the context of a marriage. Foreign citizens must present it to their consulates for passport matters.