Okay, so imagine you have a big castle. There are many rooms and people who work in it. The master of the stewards is the person who is in charge of all the people who work in the castle.
You know how mommy and daddy have a boss at their job who tells them what to do and makes sure everything runs smoothly? That's kind of like what the master of the stewards does. They make sure that all the people who work in the castle do their job correctly and that everything is clean and organized.
They also help make important decisions about the castle, like who should live there and how much money should be spent on fixing things. Think of the master of the stewards as the boss of the people who work in the castle, making sure everything is taken care of and running smoothly.