Introduction to CSS
Cascading Style Sheets or CSS is simply the addition of style to HTML. Style Sheets are a publishing conecpt designed to create a specific look and feel to a page. HTML, at its roots, doesn't have any page layout or formatting built into it. CSS is a method designed to create layout and formatting for web content. Rather than being a standard to tell you how to make your page look, however, it is a system for allowing you to define the look you want.
CSS is huge, and contains methods for defining just about everything about the look (and even the sound) of your website.
There are, however, a relatively small number of extremely common CSS elements which any good Web designer ought to know. I'll leave the full CSS specification for others to write out, while I focus on how to use it in basic web design.
For a thorough treatment of CSS, there are a number of resources available. Below are just a few of my favorites:
On with the tutorial! Here's the Basics of using CSS