The regulations that apply for your stay in Germany depend on the country that you come from.
Citizens of EU/EEA Countries
If you come from an EU member state, Norway, Iceland or Liechtenstein, then you do not need a residence permit. You can start a job and do not need a work permit.
You can provide evidence of your right of residence with your passport and certificate of registration.
Citizens of Switzerland
Citizens of Switzerland do not need a residence permit. Family members of swiss citizen have to register at the relevant Foreigners' Registration Office.
If you are not a citizen of the European Union (EU) or Iceland, Norway, Liechtenstein or Switzerland, you require a so-called "residence permit" for a stay in Germany.
The residence permit also governs whether you can engage in employment in Germany and what employment you can pursue. It sounds complicated but the the team at the Welcome Centre will gladly help you to apply for the residence permit that is right for you.