What an extremely useful site this is. CSS Help Pile has everything you wanted to know about CSS and didn't for designing web pages.
What is CSS? From Jennifer Kyrnin:
"Style sheets are a very powerful tool for the Web site developer. They give you the chance to be completely consistent with the look and feel of your pages, while giving you much more control over the layout and design than straight HTML ever did."Once you get into having CSS on any website you might be designing, you'll wonder how you ever got along without it.