1. Learn HTML/HTML5 - I can't really recommend anything here. I just sort of picked it up.
2. Learn Ruby on Rails - http://ruby.railstutorial.org/. You can probably pick up a lot of HTML and CSS from this tutorial. I spent about 50 hours working through this. You're probably looking at 80 hours or so.
3. Learn JS - http://www.codecademy.com/tracks/javascript
Once you've put about 200 hours into the the above, I'd say you're probably capable of building a working website. It won't be pretty, but it will work.
Refractor and fix from there.
- HTML5
- CSS3
- Javascript
- basics of image manipulation
- some kind of backend language (PHP, Python, Ruby, Node.js,...)
- some kind of database engine knowledge (SQL, NoSQL, both?)
- user experience planning, testing and execution
- extensive server administration
- different APIs
These are just the technical aspects, now count in the whole business side of things. 3-5 years. Probably more if you want to master all of the above.