Coming from a similar background, I second a lot of the links pointed out so far (w3schools and JQuery have been a huge help in particular). It's a great start. After that, just dive in. I started writing a chess game using canvas (part of HTML5) and javascript. It's just been a matter of figuring it out piece by piece from there. Writing lots of awful code, figuring out why it's awful, tearing it up and doing it again (Javascript: The Good Parts has been a great help).

I've managed to learn just enough html/css/javascript to be dangerous, now I'm moving on to server-side programming. What I like to do is this: Take an 11"x17" piece of paper, and write whatever it is I'm trying to learn in the centre and circle it. As I figure out what I don't know know about this technology, but need to, I draw a branch off the centre circle, for that piece of knowledge. And I continue to break it down as I go. This gives me a good visual of things I should start focussing on.

As a more concrete example, I'm using python as the backe end to my current side project. So in the centre of the page is a bubble for python. Off that I have different things I want to explore, so there is a bubble for Security, WSGI, templating engines, and SQLAlchemy. Off of security, there are bubbles for server hardening, XSS, etc..

Best of luck, there's lots of confussing technologies and non-sensical gotchas, but eventually it does start to make sense.

I've had serious reservations about content from w3schools, to the point where I now skip them entirely when they come up in a Google search. They seem like a collection of all the bathroom-wall code ever: MySQL or SQLServer specific code presented as "SQL", things that only work in one browser or another presented as the best way to do things, etc. I usually know enough to know that their approaches are misleading, and I shudder to think how many devs take them at face value.