Okay kiddo, have you ever gone into a really tall building with lots of floors? Like a skyscraper? Well, sometimes there's something strange that happens in those buildings - they skip the thirteenth floor!
Now, you might be wondering why they would do that. Is there something wrong with the thirteenth floor? The truth is, it's just a superstition. Some people believe that the number 13 is unlucky, and they don't want to take any chances.
So, instead of having a real thirteenth floor, they just skip that number and go straight from 12 to 14. It's kind of like how some people skip the number 7 when they count - it doesn't really make a difference, but it makes them feel better.
But don't worry, kiddo - the thirteenth floor doesn't really disappear. It's just called something else, like the "14th floor" or the "12A floor." So even though it might seem strange, there's really nothing to be scared of.