Okay, imagine that the military is like a big group of people who are really good at protecting and helping our country. Military administration is kind of like the grown-up job of making sure everything in the military works smoothly and everyone knows what they're supposed to do.
Just like how in school there are teachers who plan out lessons and make sure everyone knows when school starts and ends, in the military there are leaders who make plans for what the soldiers should do and how they should do it.
And just like how at home your parents make rules to keep everyone safe and happy, the military leaders make rules called regulations to keep everyone in the military safe and working together. For example, one regulation might say that soldiers have to wear a certain uniform so that everyone looks the same and it's easier to tell who's on our team.
So military administration is all about making sure everyone in the military knows what they're supposed to do, when they're supposed to do it, and how they're supposed to do it. That way, they can work together to do their important job of keeping us all safe.