Having a team website is important for many reasons. Not only is it a central resource for team information, but it improves your standing with potential sponsors and gives your team more credibility.
In order for a website to exist, you need 3 things: a domain name, hosting, and content.
A domain is how people reach your website, for instance google.com, stuypulse.com, or firstconnects.us. They generally cost less than $10 a year, and can be obtained from your hosting company. What's a hosting company?
Websites are "hosted" on servers that are connected to the internet. The hosting server holds all the files for your website, and is assiociated with your domain name. Any computer can be a server, but hosting companies have many computers optimized to host websites. You should probably search around for a good price on hosting, but keep in mind that it's usually upwards of $100 a year.
One you have your domain and hosting, teams have two choices for making websites: custom coding or a CMS (content management system). Custom coding can give you a more custom site that can be manipulated any way you want, but it requires knowledge of at least html and css. For those teams who want an easier functional site, using CMS's like Drupal or Joomla are popular choices.
Using CMS's, you can design your website's interface (within limitations) and then write content for the site. Most CMS's have extensive documentation specific to their software that will guide you through the steps of creating and maintaining your site.
If you choose to do your own coding, you have almost infinite options in what you can do. We wrote our site in PHP (PHP Hypertext Preprocessor), a programming language designed for building websites. PHP is an industry standard, and scattered around the internet are forums and tutorials devoted to PHP.
Here are a bunch of links to resources to start you off...
w3schools.com -- basically an encyclopedia of how to write the internet... amazing, really.
Valid code means that your code is standards-compliant, which means it should be displayed the same way on all standards-compliant browsers (e.g., WebKit-based browsers like Safari and Chrome).
validator.w3.org -- an online validator for HTML from the World Wide Web Consortium (W3C); it validates HTML from a URL and from local files
http://jigsaw.w3.org/css-validator -- a validator for stylesheets (CSS)
Adobe's DreamWeaver is an industry standard and has both a WYSIWYG (what you see is what you get) and a text editor mode. It's not cheap, but you might be able to get a team parent to donate a copy.
Notepad++ is a text editor with syntax highlighting for Windows.
For those of you awesome enough to use a Mac (it's not just me, right?) Komodo Edit works well (this site was written in it).
Of course, you can use any editor bundled with your OS, like Notepad, GEdit, Emacs or XCode.
Subversion is a version control system - this allows you to upload code where others working on the same project can see it. It's also helpful when you want to access an older version of your code, especially when your code is too obfuscated or otherwise broken beyond repair.
Our subversion repository (for both robot code and website code) is here: http://stuypulse-svn.dreamhosters.com/
TortoiseSVN is a Windows shell extension that allows you to use subversion with a graphical interface.
There are also command-line subversion interfaces for Linux and Mac.