Welcome to the long, never-ending road of web development :S.
To start off as everyone has said it's going to be HTML (HyperText Markup Language). Or more specifically xHTML (XML complaint HTML). Most the formatting, forms, everything you see in HTML is based on simple HTML.
But HTML will only bring you so far. If you want colorful, modern pages you will start learning CSS (Cascading Style Sheets). CSS is definitely the direction the web is heading now from strict HTML. People replace HTML tables with CSS divs. There's a lot of reasons now but a lot of it is it allows you to allow more people to see your site in various browsers all in the same ways.
Your next step would most definitely be JavaScript. The appeal to JS is flashy, somewhat dynamic functions. It has nothing to do with the formatting of your website, yet the functionality. Think of HTML/CSS as the body of your car and JS as the engine. Many designers skip JS. I DO NOT RECOMMEND skipping JS.
After these three languages the paths you can take are numerous. The one I recommend is PHP/MySQL.
Remember I said to think of JS as the engine of a car. Well think of PHP as a 1,500 horsepower monster truck engine while JS is the 80 horespower engine to your mothers Saturn. PHP is more powerfull, functional, and dynamic than JS because it is a Server Side Programming Language rather than a client side programming language. This means when you're coding in PHP your code is parsed or read through and executed by the web server rather than the users browser. So you have room for more functions, more processing power, speed, etc.
PHP also allows you to connect to databases such as MySQL. Databases allow your website to display dynamic content instantly. For example. When you posted this topic your post, the time of the post, the posts title, etc. was all entered into the webmaster-talk forums database. Then when I came along and read your post all the info that was entered is retrieved then displayed to me by PHP requesting the post from MySQL. Without databases and server side programming web sites would never be dynamic. Users wouldn't be able to communicate and interract in the ways we are all so comfortable with now.
After PHP/MySQL you can learn ASP, AJAX, etc.
It's a good idea durning all of this to learn more about web protocals such as HTTP, IP, RSS, Telnet, FTP, DNS, etc. They're simple to learn about and help you emmensely because you understand how websites and computing work so the enviroment you will constantly be working in will be much less intimidating.
After all this you can start learning advanced, extrmely powerfull langauges that often times have nothing to do with the web, rather actual applications. Some examples would be C based languages, VB, Java (DIFFERENT THAN JAVASCRIPT!!!).
This is all very confusing and I'm extra out of it today (looooong night last night :P :P :P) so if you need any help whatsoever PM me or MSN me. I'm always willing to help

. It's always fun to see someone learn the web.
Good luck.