Explain · Like I'm five version
Black holes in terms of a plumber
A black hole is like a very grumpy plumber who has lost his favourite spanner down the sink.
Imagine a kitchen sink where the plug hole is so big that it pulls in your plates, your spoons and even your favourite pair of wellies. This plumber is so strong that he pulls everything into his pipe with a giant, invisible magnet. Once your toy car slides down into the dark, twisty pipe, it is gone forever. The plumber does not give it back, not even if you ask really nicely or offer him a custard cream.
The pipe gets so crowded with all your lost things that it becomes heavier than the whole house put together. Because the plumber has squeezed so much stuff into such a tiny space, the pipe gets super tight. It becomes a place where even light cannot shine, just like when you hide under your duvet with a torch and turn it off. The plumber sits there in the dark, watching the pipe grow and grow as he keeps pulling in more missing socks.
This plumber is very busy because he keeps on cleaning up the galaxy. He takes in all the loose space dust and wandering stars that nobody wants anymore. He does not stop to have a cup of tea or a quick nap on the sofa. He just keeps on working until the whole universe is tidy and there is nothing left to trip over on the floor.
Where the analogy breaks downthe plumber cannot actually crush a star into a tiny dot inside his pipes.