The only code I have a wide understanding of is HTML. I know nothing else. To be honest I've never needed or looked into anything else. I was just wondering is there anything else that is as "advanced" as HTML mark-up?

Also, is CSS and other coding hard to learn?

HTML is probably one of the simpler coding languages you will find out there. Other languages aren't necessarily hard, but you just have to be willing to take the time to learn them.

i like html, css, and javascript. rightnow I'm learning actionscript 2.0

HTML isn't really "code", but markup -- a way of labeling this so that a browser can read it. CSS isn't code, per se, either, but again, a markup-type language designed to style HTML (and it's variants). Javascript, on the other hand, is a coding language, but is confined to browser-running only (unless you do some other fancy things, but 99.999....% is used in browsers only).

Personally, PHP is what I'd recommend. It runs on the server and allows you to output, amongst other things, HTML, CSS, and Javascript, but it unleashes a whole new world of options for you. It's fairly easy to learn and you can bypass many of the more advanced concepts like type-checking, pointers, etc which lower-level programming languages require.