Okay kiddo, so you know how everything in the world is made of tiny particles called atoms? Well, some of these particles have an opposite, like a mirror version of themselves, and we call them "antiparticles". When an antiparticle meets its particle, they both disappear in a big burst of energy.
Now, imagine we could capture these antiparticles and use them as fuel for a special kind of rocket. When we mix them with normal particles, they would destroy each other and create a huge amount of energy that could make the rocket go really, really fast. We call this an "antimatter rocket".
But here's the tricky part. Antimatter particles are very hard to find and capture, and they only exist for a very short time before they meet their particle and disappear. Plus, it takes a lot of energy to make them in the first place. So making enough antimatter to fuel a rocket would be super expensive and difficult.
But if we could figure it out, an antimatter rocket could take humans to places in space much faster than regular rockets do. Maybe one day we'll have the technology to make them work, but for now, it's still mostly a cool idea that scientists are working on.