Bangle.js 2: How do I use it as delivered? Is there any user documentation?

Hi.
First to do is read the doc here to know what it is all about, what is inside and what can be done with: http://www.espruino.com/Bangle.js2

Then, you can connect your Bangle.js 2 and customize it with the apps you want: https://banglejs.com/apps/

As is, it already provides a lot of possibilities, but remember, it is meant to run you own apps. To know how to do that, you can follow this very good example:
https://www.espruino.com/Bangle.js+First+App