To begin someplace, CSS stands for Cascading Style Sheets. It makes it possible to style your homepage faster than if you use tables, (then you have to change ALL the codes!) In css you just change the colors for example your header, and voila all of your headers has the same color!
Under is the code for the css, copy it and paste it into your homepage.
The picture under has an explanation of each part of the css
Now you can add the headers to your site.
The codes i use the most is h1, h2 and h3.
Here you are;
If there is something you don't understand, add me on msn, and i'll explain it in depth for you :)