Okay kiddo, have you ever heard of deed poll? It's a legal document that helps people change their name if they don't like the one they have.
Let's say you were born with the name John, but you decide you want to go by Jack instead. You can use a deed poll to change your name officially.
It's kind of like a grown-up version of playing make-believe. Except instead of pretending to be a superhero, you're pretending to have a different name. But with a deed poll, that pretend name becomes real!
The deed poll is a fancy piece of paper that has your old name and your new name on it. You sign it, and maybe some grown-ups sign it too. Then, voila! You are now legally called Jack instead of John.
It's important to remember that a deed poll only changes your name - it doesn't change anything else about you. You're still the same person, with the same family and everything. But now, you get to introduce yourself to people as Jack!