Just starting HTML/CSS?
Start here :)
HTML and CSS are the standard (very simple) languages to make web pages. HyperText Markup Language defines the structure of the page and its content, while Cascading Style Sheets determine how it all looks and how it gets arranged on the page.
What about XHTML? DHTML? How many kinds of HTML *are* there?
There's a simple language known as XML ("eXtensible Markup Language") that's very similar in looks to HTML, but has stricter rules that make it easier for computers to read. XHTML is simply the idea behind applying some of those strict rules to HTML so that your code gets even cleaner. Many developers prefer XHTML, but that's something to worry about only once you've learned this stuff.
How to get started!
There are GUI point-and-click editors like Dreamweaver and iWeb to make websites, and in a pinch, they can be useful to see how a certain design might be coded. But there's one thing you should know, right off the bat:
Real web developers do not use point-and-click programs like Dreamweaver. They write their own code.
So if you're serious about learning this stuff, grab your favorite text editor, sit down with a beginner's tutorial, and get rolling! You'll find some really awesome guides below, so follow them as best as you can, then try your hand at making something original. When you run into a problem, come back here! Search the forum, and if you can't find what you need, ask away.
When it comes to web guides, there's no beating Tizag.com. But W3Schools.com has some good primers as well -- so take a look at both, and go with what you like!
Tizag's Beginner HTML Tutorial
Tizag's Beginner-to-Advanced CSS Tutorial
W3Schools' HTML Tutorial
W3Schools' XHTML Info
W3Schools' CSS Tutorial
W3Schools CSS Reference Sheet <-- This thing's a lifesaver!