How to make my web chat app like omegle? [Node.js and Mongodb]

I have made a very simple chat app using Node.js and MongoDB where as soon as you enter the app you are put in the same room and all messages are emitted to all users. How can I make this like Omegle where the users are randomly allocated to another 'Stranger' and not in a group. I am new to all of this so I would appreciate it if you could try to explain in layman terms.

Thanks!