Imagine you have a really big puzzle with lots of pieces. Now imagine that instead of putting the puzzle together in one giant cluster, you put each puzzle piece in its own little box. That's kind of like what it means for a space to be a-paracompact.
When we say a space is a-paracompact, that means we can cover the whole space with little boxes, called "open sets," in such a way that each box only overlaps with a few other boxes. This is kind of like how each puzzle piece only fits with a few other puzzle pieces, but we can still put them all together to make the whole puzzle.
Why is this important? Well, it turns out that a-paracompact spaces are really good for doing all kinds of math and physics stuff. They let us do things like integrate functions (which basically means adding up a bunch of numbers) or solve equations in a nice way.
So, just like putting each puzzle piece in its own little box makes it easier to put the whole puzzle together, having an a-paracompact space makes it easier to do math or physics in that space.