You click the login button, put in a gmail address, and that's it.
The advantage of this is that you get the ease of logging in with an account you already have, but Google cannot track the fact that you logged in to any specific site... they only know you logged into Persona.
You can now sign in to any Microcosm site using Gmail.
http://identity.mozilla.com/post/57712756801/persona-makes-signing-in-easy-for-gmail-users
You click the login button, put in a gmail address, and that's it.
The advantage of this is that you get the ease of logging in with an account you already have, but Google cannot track the fact that you logged in to any specific site... they only know you logged into Persona.