Okay, so let's say you have a really important toy that needs to be taken care of because you can't do it yourself. But the person who usually takes care of the toy is not able to do it for some reason. So, someone else who is very trusted and knows how to take care of your toy comes to help out. This person is like an apostolic administrator.
In real life, this can happen with important things like a church or religious organization. The usual leader of the church may not be able to take care of their duties for a period of time, so someone else comes in and takes care of things until the original leader can come back. This person is an apostolic administrator, and they are chosen by the pope or another important religious leader to make sure everything runs smoothly while the regular leader is gone.
The apostolic administrator helps make decisions and manage the church or organization and keeps things going until the regular leader can come back.