In a nutshell there are three basic things to learn:
- HTML for your basic page structure
- CSS for making the page look good
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/CSSPeople all over have been raving about this series on Tuts+ that goes through both HTML and CSS:
I also looked over the course index myself, and I think it looks great.
Interactive for HTML/CSSAnother 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:
Another option is YouTube - this fellow has a really nice series of introductory tutorials that are friendly and approachable: