How do I make my custom character to be any player who joins, to be their avatar in my game?

If you don't know what I mean. What I am asking is that How to make a custom character that you created (and grouped, named each part and the model itself) to be every player's avatar when they join. (I am using a simple yellow naked face-less character.

Name your custom character StarterCharacter and put it in the StarterPlayer

see this article about custom chars