Ok kiddo, let's imagine you have a toy box. The toy box has a certain size, right? It's not too big or too small, it's just the right size to hold all your toys. That's what we call "capacity".
Now, scientists also work with things that have a certain capacity. They use a special unit to measure it, called "square kilometers", or "km2" for short. It's like having a giant toy box that can hold lots of things.
Sometimes, scientists need even more space to study things. So they use "cubic kilometers", or "km3" for short. It's like having a toy box that's not only big on the outside, but also very deep inside, so you can put a lot more toys inside.
These sites are places where scientists can do research and collect data about different things. Think of them like your toy box, but instead of toys, they hold things like rocks, water, or even air. Scientists can use these measurements to help us understand more about our world and how it works. Pretty cool, right?