You should learn HTML so you can program your pages. You need to decide if your going to do content, programming, sys admin or manger.

List of client side programing languages:
HTML
CSS
XHTML
DHTML -- AJAX replaced this for the most part
AJAX
JavaScript
XML

List of Server side programing languages:
SSI
Perl
Java
PHP
Coldfusion
ASP and ASP.net

List of servers or app server you might want to know.
JES (Java Enterprise Server)
coldfusion -- app server can also be web server.
PHP -- app
apache web server
IIS -- Microsoft's web server

List of database stuff
XML
MySQL
Oracle
Sysbase
Access -- not really for professional web pages.

I do sys admin work for web portals it a lot more involved then you can know.
if you know nothing then learn HTML and CSS. Get a homepage or blog and learn how to maintain and design it. If your interested in learning webservers and app server put a webserver on a pc at home and make some pages with it.
Also if you want to do cool stuff you need to learn a little database.

You can learn DB and server side scripting or programing on some webhosting plans. Webhosting sites will charge if you do any thing more then a static site.

It is best to learn a little of every thing and then pick a specialty.

Hope this was helpful

Learn to empathize with others. This is the single most important trait of a webmaster that comes with experience. You can always learn the technical stuff mentioned above, but to be a really good web master you need to know your audience and anticipate your needs. Everything on the web revolves around content that someone is looking for. If you can figure out what your audience needs then you can build out a community which is vital for achieving any other goal.

All the technical details are a waste of time if you don't have something that someone is seeking out.