AngularJS is a great javascript framework. Declarative programing you tell angular what to do instead of how to do it, with less code to write and maintain, code well organized. ex: www.truecar.com
It has fantastic community support.
How does it work?
user makes a request on url to the server that sends back a response with the entire angular application, this thanks to the fact that angular is made entirely in javascript. The app files will not be sent again. The app is able to make request for data to the server with AJAX for small amount of data. Backbone and Ember work in a similar way.