Okay kiddo, so the Worldwide Military Command and Control System (or WWMCCS for short) is like a giant brain that helps the military all over the world work together.
Imagine you and your friends are playing a game of tag, but you're all in different parts of the park. It would be hard for you to communicate with each other and decide on a plan to catch the person who's "it".
Now imagine that you all have walkie-talkies to talk to each other. That makes it a lot easier to work together and catch the person who's "it". The WWMCCS is kind of like a really big and fancy walkie-talkie system for the military.
It helps them share information, like where the bad guys are, what they're doing, and how to stop them. It also helps commanders make decisions about what to do next.
So, just like using walkie-talkies helps you and your friends work together and catch the person who's "it", the WWMCCS helps the military work together and do their job of protecting their countries.