Okay kiddo, so imagine you have a bunch of friends and you want to send them all the same message at once. Instead of typing their names one by one every time you want to send the message, you can make a list of all their names together. This is called a distribution list.
It's like making a list of all the people you want to invite to your birthday party - instead of telling each person separately, you tell them all at once by sending the invitation to the list.
So when you have a distribution list, you can simply send your message to that list and it will go to everyone on the list at the same time. It's an easy way to send messages to lots of people all at once without having to type out each person's name every time.