In a nutshell there are three basic things to learn:
- HTML for your basic page structure
- CSS for making the page look good
- JavaScript to bring that page to life
How you go about learning these depends a little bit on your past experience, and also on how you like to learn. You can always get a book (and there are many), but I think it's better to learn a little, try a little, lather, rinse, repeat. More of the usual course style of learning. But do you like video instruction, or do you prefer to read it?
Video for HTML/CSS
People all over have been raving about this series on Tuts+ that goes through both HTML and CSS:http://learncss.tutsplus.com/
I also looked over the course index myself, and I think it looks great.
Interactive for HTML/CSS
Another way to learn is the online interactive format used by Codecademy. If you think you might like that style better, try their excellent web track here:http://www.codecademy.com/tracks/web
Video for JavaScript
I've read mixed reviews on the JavaScript videos on Tuts+, but have heard good things about Treehouse (http://teamtreehouse.com/join/start-learning-free). It's a paid service, but you get 2 months free and it's not terribly expensive after that ($25/mo).Another option is YouTube - this fellow has a really nice series of introductory tutorials that are friendly and approachable:
http://www.youtube.com/watch?v=yQaAGmHNn9s
Interactive for JavaScript
Again the interactive format on Codecademy is really nice and you can find their JavaScript course here:http://www.codecademy.com/tracks/javascript