While raising him, you teach your German Shepherd what is and what is not acceptable behavior.
This is different in each family.
In one family, for example, nobody minds if the dog sleeps on the couch or is present during dinner, while in others this is not permitted.
However, there are rules every dog should know.
Pulling on the leash, attacking other dogs, and chasing cats, of course, can never be allowed by you.
Your German Shepherd should also learn that he may never, ever jump out of the car or walk out the door in front of you, before he has been commanded to do so.
The command "wait" is perfectly suitable for this.
Very protective German Shepherd Dogs may bark more than necessary, and you may not accept that, either.
Bumping against people, doors, and cars, knocking over children, growling at the feeding bowl or bone, begging for food - there are all things you should never tolerate.
Remember that teaching good behavior while the dog is still young and uninhibited is much easier than breaking unwanted behavior that has developed over the course of time.
A difficult dog that obeys poorly and goes his own way was not born like that but was made so by a master who has never been consistent , and has not had enough time or insight to devote to the proper raising of a dog which may not have the easiest character.
However, if you are consistent, knowing the right moment and the right way to punish and reward, then your dog will soon adjust to your rules.