De jure means "by law." Imagine you're playing a game with your friends, and you make a rule that everyone has to jump up and down three times before they can pass the ball. That's the law of the game - you all have to follow it because you agreed to it.
De jure is like that game law. It means something is officially recognized as being true or legal because it's written down in the law. So, for example, imagine a country has a law that says everyone has the right to free speech. That means de jure, people can speak their minds without getting in trouble because the law says they can.
So, the next time you hear de jure, just remember it means "by law" and it's like the rules of a game that everyone has to follow because it's written down.