I'm not 100% convinced this isn't automated spam, but anyway...
HTML and CSS are two very different things, and they're used in tandem together to develop most sites. CSS deals with the style side of things, i.e. how the elements should be displayed on a page, and HTML deals with the content.
If you want any more info you'll have to provide much more detail - but I'd really suggest Google as a first stop. There's lots of resources out there on both of the above.