Okay, so imagine you're playing a game and you need to see what your friends are doing on the other side of the game board. But you can't see them because they're too far away. That's kind of like what the military has to deal with. They need to see what's happening on the ground from really high up in the sky, but they can't just look out of a regular airplane window because they're too high up.
That's where the E-8 Joint STARS comes in. It's like a really big airplane that has fancy cameras and other equipment on it. When it flies over an area, it can take pictures and use its equipment to figure out what's happening on the ground. It's kind of like a big spy-plane!
The "E-8" part of the name comes from the fact that it's the eighth version of this type of plane that the military has made. "Joint" means that it's used by multiple branches of the military (like the Army, Air Force, and Navy). And "STARS" stands for "Surveillance and Target Acquisition Radar System," which is basically the fancy equipment it has on board that helps it see what's happening on the ground.
So in summary, the E-8 Joint STARS is a really big airplane that has cameras and other fancy equipment on it. It flies high up in the sky and helps the military figure out what's happening on the ground by taking pictures and using its cool toys.