Where to start when wanting characters to load into the game with my game character?

How do I make avatars that loads into my game spawn with the character I would want
them to spawn in as (i.e: a block or a mouse). I was hoping someone could grant me
relevant links that could help me. This is a beginners project I am going to work on.

Take the model you want as the character, name it StarterCharacter, and put it inside of StarterPlayer.