Okay, so you know how sometimes when you play pretend, you might say "I'm the queen!" or "I'm the king!"? Well, some people take this game really seriously and they don't want to stop being the "king" or "queen" even when they grow up. They call themselves a "self-proclaimed monarch" and they believe they have the power to rule over a certain group of people or territory.
But just like in a game of make-believe, being a self-proclaimed monarch doesn't mean you actually have any real power. No one else has to listen to you or do what you say just because you say you're the queen or king. In fact, most people don't take self-proclaimed monarchs very seriously because they haven't been chosen by anyone else to be a leader.
So, being a self-proclaimed monarch is kind of like being a pretend leader. It might be fun to imagine having a crown and ruling over a kingdom, but in real life you need more than just saying you're a king or queen to actually have any authority.