Codecademy is pretty awesome if you really want to start with the very basics. The lessons they have so far cover Javascript, but the features they teach you span most languages.
http://codecademy.com
When I started out, though, I had a clear vision of what it was I wanted to do, bought a book, and started hacking away. I learned best by jumping in head first with the hard stuff, but I realize a lot of people learn differently than I do. I would say that if you find the Codecademy courses too easy or boring, you should try my approach instead.
As far as what to learn...it kind of depends on what you're trying to build. Back when I was teaching myself, I was using PHP and MySQL, but the world appears to have mostly moved on from the LAMP stack of yesteryear. I'm partial to Python these days, but I've always enjoyed Java as well. Javascript has blown up in a huge way in the past couple of years and platforms like Node.js have only made it that much more practical. If I were to start learning web development today, Javascript is probably where I would start.