Distributed systems are like a team of kids sharing toys.
Imagine you have one big box with all your toys. If only one kid can play with it, that's slow and boring. If the box breaks, you have no toys.
Instead, you give each kid a little box with some toys. They can play with their own toys fast, and they can share with friends.
A distributed system is many computers working together like that team of kids:
Many computers = many kids with boxes
Each has a piece of the job= each kid has some toys
They talk to each other= kids pass toys back and forth
If one kid goes home= the others keep playing
More kids = faster= you can add more boxes to do more work
The tricky part is making sure everyone agrees on the rules, doesn't lose toys, and doesn't play with the same toy at the same time.
So it's just lots of little computers helping each other so things are fast, don't break easily, and can grow big.