Okay kiddo, so you know how when you go to school, there's usually a principal who's in charge of making sure everything runs smoothly? Well, when the leader of the Roman Catholic Church (who is called the Pope) travels somewhere, there's someone who is in charge of making sure everything runs smoothly for him. That person is called the Prefect of the Pontifical Household.
The Prefect of the Pontifical Household is a very important person in the Catholic Church. They are responsible for making sure that the Pope's schedule is organized, that the people who meet with him are chosen carefully, and that everything is ready for important ceremonies like church services or meetings with other important people.
In a way, the Prefect of the Pontifical Household is like the "principal" of the Pope's household. They have a big job to do, but they do it to make sure that the Pope is able to focus on doing the important work of leading the Catholic Church.