http://www.w3schools.com is a good place for beginners to get started. For more detailed information than they provide, you'll need to refer to the correct specification on W3.org. There are many other resources out there too, like I found this one helpful for XHTML 1.1: http://learningforlife.fsu.edu/webmaster/references/xhtml/tags/index.cfm
One big issue you'll come up against is the fact that browsers aren't all compatible, so you'll need to build your sites accordingly. It may be helpful to install multiple browsers on your computer so you can test sites out. The best site I've come across for helping you with intercompatibility is http://www.quirksmode.org His compatibility tables are very helpful.
I'd also go ahead and install a personal web server, like Apache.
If you plan on doing any server-side scripting, which is very likely and useful, you'll probably want to install and learn PHP to some extent. It's the most popular and it's free and has good resources too, even though I don't think too much of it as a programming language. I do like it better than ASP.NET, though.
Besides basic HTML / XHTML, you'll need to learn CSS. That's essential for getting sites to look how you want them to look.
Javascript is what you'll need for client-side scripting, so make sure to learn that pretty well. For good DOM-programming, you'll want to use XHTML instead of HTML. I prefer to use XHTML 1.1 Strict.
You'll want to find a good text editor to use for coding (I like Crimson Editor, but there are other good ones too). Get some experience using photo-editting software for image creation and manipulation. You'll use it to create backgrounds and gradient effects too. I use The Gimp and PhotoFiltre among others, depending on what I'm doing.
If you want to host media like videos or audio, you'll want to figure out how to embed flash objects in your pages and get them to work with your media. You don't necessarily have to know anything about Flash in order to use a flash file, like a music player or something, but you will if you want to create your own flash animations.
Scaleable Vector Graphics (svg) is still a developing standard without good support, but it has its advantages for some things, so you might study that too if you have the time and curiosity.
On a more basic note, if you don't know much about the HTTP specification, I think it will be helpful to get the basic gist of how things like requests, responses, headers, URLs, forms, and cookies work.
bob b makes some good points. dhvrm is somewhat right in that that's how a lot of people do it to make great-looking sites without much effort, but that often just sucks people into being dependent on and locked into using a CMS for everything instead of doing any real programming or understanding things well enough to fix problems that arise. His comment "Once you know how to make things pretty, then you can focus on how to make them well." seems rather like putting the cart before the horse. "Once you paint the barn bright red, then you can work on shoring up the foundation and replacing all the dead wood."