Within the first weeks after arriving in Plön/Kiel, you have to register your new place of residence with the local Residents’ Registration Office. Only your passport (with the eventual Visa) is needed for this registration. You will receive a registration paper, which is an important document, so keep it. Ask if you need help with this, the WO will be happy to accompany you to the Office.
Any change of adress during your time in Germany has to be re-registered. Before you leave Germany, you will have to officially cancel your registration with the local Residents’ Registration Office.