Why is it that when you push two pieces of wood together, they don’t smush together and become one smaller piece of wood? Because the atoms that make up the pieces of wood push against each other, repel each other. They want to own their own little bit of space. They resist being smushed.
But they can only push back so hard. With enough force, you *can* smush atoms together, breaking them down into smaller things. Those smaller things also don’t want to be smushed together, but with enough force, they will too. Everything will, with enough force.
A black hole has, in its center, a singularity. It’s where there is so much gravity smushing things together, that no force can resist it. They smush down really small. In fact, if you’re picturing a very small ball, ask yourself: why is there even a ball? Why wouldn’t gravity smush it into something *even smaller*? And it does. It smushes everything until it’s got no size- it’s width is zero, nothing, nada.
But it still has all the mass, the weight, of all that stuff. So it weighs more than a star does, but it’s infinitely small. This is a singularity.
When we try to do the math related to physics, all of the math stops making sense when you’ve got a singularity. That’s what makes it interesting.