Alright little one, have you ever played a game where you have to count how many things you have? Like how many toys you have in your toy box? That's basically what an inventory is, it's just a list of all the things you have.
Now, Henry VIII was a very important king a long time ago in England. He was like a big boss who owned a lot of things, like fancy clothes, shiny jewelry, and big castles. But he also owned a lot of other things like cows, chickens, and all sorts of food.
So, one day someone decided to make a list of everything he owned, from the big things like castles, to the small things like how many spoons he had. They called this list the "Inventory of Henry VIII" and it was made so that everyone could keep track of his things.
The inventory was a very long list and it took a lot of people a long time to make it. But once it was done, people could see just how much Henry VIII had and how rich he was compared to everyone else.
So that's pretty much it, an inventory is just a big list of everything you own, and Henry VIII had a LOT of things.