I seem to recall seeing on HN a few months ago some tool or library that would allow you to easily create a sort of welcome walk-through for your web application. I think it used tooltips that would one-by-one show you different parts of the UX. My google-fu and hn-searching abilities are failing me however. Can anyone remember that or find the link?
What you're looking for is commonly called a tour. Since it's web-based, it will be implemented in JavaScript. Searched HN for those terms, found this:
http://usablica.github.io/intro.js/