If you own a car in Germany, you must pay a vehicle tax (Kraftfahrzeugsteuer or Kfz-Steuer) every year. The cost depends on the type of the vehicle, and the size of its engine. Scooters under 50cc do not pay vehicle tax.1
You get a vehicle tax statement (Kraftfahrzeugsteuerbescheid) every year by post. It tells you how much vehicle tax you must pay.
Vehicle tax calculator (in German) – Ministry of Finance