Hello I dont know how to add my friend in to my world as na administrator.
Hello Peplaus,
I'm sorry no one has answered your question, and having only recently discovered this platform I'm not the most knowledgeable. I had the exact same idea, but it looks like there's no way to collaborate before a game is published. That said, it looks like people have figured out how to collaborate using templates.
This page has more information on it.