I bought “My Book Live 2T” and I want to give a user rights to read the entire drive but create a Folder that they are the only one to have full access to.

That’s fine… you can do that.

You will need to create a “Private Share” for the user. 

You can do this through the User Interface by creating a new User. There is an option to create a private share for the new user, check that box.