These three directories are a few demo projects giving a starting point for learning/using (in particular) angular.js and require.js, two of the libraries we're going to be using across this project.
to see these webpages live, you can either use your own http server, or you can use node.js and the provided web-server.js, which I highly recommend.
Node.js is, contrary to what it's name would suggest, not a javascript library, but rather a javascript interpreter (with a few extentions), built for running javascript in a server-side environment. If you do the full angular tutorial, they also recommend you install node.js in order to do unit-testing.