Okay, kiddo, so an organ stop is a special button or lever on a big musical instrument called an organ. When you push or pull the button or lever, it makes certain pipes inside the organ play different sounds.
It's kind of like a very big toy box full of different toys, but instead of toys, it's full of different musical sounds. Each stop makes a different group of pipes play a different sound. So, for example, there might be a stop that makes the pipes sound like a trumpet and another stop that makes the pipes sound like a violin.
The musician who is playing the organ can use these stops to create all sorts of different musical sounds and textures, almost like painting with different colors. It's a really cool and important part of playing the organ!