You can choose to log in on plug.dj by clicking on the Log In button located at the top-right of the homepage, where you can log in with either Facebook or email.
If you do not have an account, you must go through the quick site walkthrough that appears when you first visit a community on the site to sign up.
Simply go directly to a room ( e.g. plug.dj/radiant ), complete the tutorial, then click Sign Up - It's Free at the bottom-right corner of the screen.
You'll have the option to sign up with an email address or Facebook account at that time.