hello.js: what to do with the redirect uri

I'm developing a Backbone/Marionette Javascript application and I want to use hello.js to manage authentication via social media.

I have some trouble that may seem pretty obvious for you, but I can't figure it out.

hello('facebook').login({  
    scope: 'email', redirect_uri:"fb-redirect"}, function(auth){ console.log(auth) }, function( e ){  
    alert("Signin error: " + e.error.message );  
});  

By executing the standard login method, I get redirected to a page in a popup that I defined after having provided the necessary authorisations.

But I don't understand what I'm supposed to do with the redirect, I don't understand why I need it.

When closing the redirect popup, it mentions that the login was cancelled.

I just want to receive an access_token back from the Facebook server and the basic user data such as email, first name, last name, etc...

Could you clarify this for me? Thanks.