Some useful sources for learning more about CSS is www.w3schools.com/css/ and www.css.nu/
To see some examples of the wonderful designs that can be made by using CSS for making websites, check out www.csszengarden.com.
CSS based designs give you more freedom in how your website is layed out, and it will load quicker and save you bandwidth.
CSS stands for "Cascading Style Sheets". The Styles determine how HTML and XHTML elements are displayed.
Building websites with CSS is more and more becoming the standard. The "old" way of creating web page layouts was by using HTML Tables, which creates many problems in itself. Table-based layouts create problems for accessability and flexible layouts, among other things.
CSS and style sheets are here to stay. Table-based layout of web pages should be avoided - it is (or should be) a thing of the past.
How to stop snoring