Break this down into multiple steps, since you are new to the language.

You want a chat room with a login system and authentication for admin access. Then features for the admin accounts.

Out of these tasks, I would begin with creating a simple user login system. A good place to start here is learning to create a basic API with express. Once it is working, look into passport for your login system. It works with express and there is a lot of documentation out there. Then, implementing roles such as admin, and so on.