You can use your car in Germany with a foreign license plate number for one year. After that you need to apply for a German plate number, which means that you have to bring your car to the so called “TÜV“. There your car will have to pass a roadworthiness test and an exhaust-gas analysis. If you have the TÜV-Certificate, you can get your German license plate at the “Zulassungsstelle” at the town hall (“Bürgeramt Halberg“, Kurt-Schumacher-Straße, 66130 Saarbrücken ).
With your driver’s license it is more difficult: Depending on the country you are from, you may be able to use your national driver’s license, you can use your national driver’s license but need a notarised translation, or you will have to pass a driving test after six months. Please check with the local “Bürgeramt” as to which regulation is appropriate to your personal situation.