This was the confusing part when I first ran couchapp to create a new app, I couldn't really see where the "entry point" of the app was. In the hope that it might help someone else I'm going to present a quick overview of the default setup.
The index.html page is a static attachement, and the user starts by requesting it with their browser.
By default this will use the div with the id items, and will attach an evently widget to it.
The evently widget that is attached will then either have an _init event, or a _changes event, either of which will be immediately run by evently.
This event will usually make a couchdb query to get data to transform to HTML and present to the user (see part three for how this works.)