Okay kiddo, you know how sometimes things can be really confusing and people might not agree on something? Well, when it comes to talking about "facts on the ground," it means that people are talking about real things that are happening right now, in the world, that everyone can see and agree on, instead of just talking about ideas or opinions.
So, imagine you and your friends are playing a game of soccer on the playground. You can all see that there is a ball, there are goals, you are all running around and trying to score points. Those are all "facts on the ground" - things that are really happening and everyone can agree on them.
However, if one of your friends says that the ball is actually a giant watermelon, that's not a fact on the ground because it's not true. The ball is a soccer ball, and that's what everyone can see and agree on.
So, when people talk about facts on the ground, they are talking about real, concrete things that everyone can see and agree on, instead of just talking about ideas or opinions that might not be true.