A particle is a tiny little thing that you can't really see with your eyes. It's like if you blew up a balloon really big and then let all the air out slowly. You would see little bits of air flying around in the room. Those bits of air are particles!
Particles come in different shapes and sizes. Some are really small, like the ones that make up an atom. And some are bigger, like the ones you can see in a dust cloud.
Scientists study particles because they can tell us a lot about how the world works. For example, some particles can create electricity when they move around. Others can give us light when they bump into things.
So even though particles are too small for us to see, they can still have a big impact on our world!