Dog obedience is a competition, where you and your dog enter a ring with a perfect score and follow the commands given by a judge. You lose points whenever you or your dog do something wrong. If you end up with enough points to qualify (or pass), you earn a leg towards a title. The judge will ask you to do exercises such as heeling, stays, retrieves, recalls and other things depending on the venue and level.
German Shepherds Dogs are well suited for obedience competition because of their loyalty, athleticism and intelligence. To prepare for this dog show you and your dog should go to training classes. There you both learn what to do and how to get along together in the ring. The classes are fun and you meet others trying to gain control of their dog and you grow in knowledge and ability together. Your dog becomes a canine good citizen (there is even a certificate for this) and you become familiar with training techniques that will be used throughout your life with your pets.
Showing dogs in obedience is a team sport. You must learn what to do and so must your dog. Obedience is a foundation for all other dog sports. You must have some obedience before you can do agility, herding or even therapy dog work or other activities. This is a greta place to start with every dog.