So in France, there are people called public prosecutors. Their job is to make sure that people who break the law are punished for what they did.
Think of it like this: Imagine you have a toy that you really like and someone takes it away from you without your permission. You would tell your teacher or your parents, and they would talk to the person who took your toy and try to make them give it back or say sorry.
The public prosecutor's job is kind of like that. They investigate when someone does something wrong, like if someone steals from a store or hurts another person, and they decide if that person should go to court and be punished for what they did.
Sometimes, the public prosecutor might talk to the person who did wrong and get them to agree to do something to make up for what they did, like paying a fine or doing community service. Other times, the public prosecutor might need to take the person to court and have a judge decide what punishment they should get.
So basically, the public prosecutor's office in France is like the "teacher" or "parent" who helps make sure that people who do bad things are held accountable for their actions.