How do i Make a custom "StarterCharacter"?

I'm making a game where you don't play as the default player model and I was wondering how you change it. I have seen tutorials on YouTube about how to do it (https://www.youtube.com/watch?v=AMk-pBlxgNQ&t=106s

but whenever I'm animation the rig I cant rotate the body parts. If anyone knows how to solve my problem or even just another way of making custom player models please tell me.

Thanks.