Of course, this assumes that you have already installed express 4.0 in your application.
The concepts involved are pretty simple.
Express lets you spawn routers using the Router() constructor (as seen in step 1). Think of each router as a place where you can specify handlers for a collection of sub-urls. These handlers may be for any of the HTTP methods. (as seen in step 2).
Once you have specified the handlers you need, simply associate the router with a base-url, which is most likely to be relative to the root ( as seen in step 3).
At runtime, express combines the base-url and the sub-url to determine the appropriate route handling function.