I am paid social-welfare benefits by the Arbeitsagentur. When I work beside of that - how much money do I keep?
If you are living in a public accommodation you have to pay back part of your salary. Generally spoken you always should go to the Job center with your work contract before and speak with your Berater.
What is a Berater (literally adviser) in this case? : If someone is registered at the Job Center they will be assigned to a case worker and they should speak with this person regarding contract questions.