Okay kiddo, imagine that you have a big castle with a big gate that keeps bad guys out. Now, you have many people who want to come in and out of the castle. So, you need someone to control who comes in and goes out. That person is called the master of the doorkeepers.
Just like you have teachers in your school who make sure only students and staff come in, the master of the doorkeepers is like the boss of the guards at the castle gate. They make sure only people who are supposed to be in the castle can enter and only people who are supposed to leave can exit.
It's a very important job because it helps keep everyone safe and makes sure everything runs smoothly. So, the master of the doorkeepers has to be very responsible and trustworthy.