Your personal web space is located in your home directory on Apollo or Athena under public_html. It is available via the Web at www.cs.virginia.edu/~yourusername/.
CGI is available for your use; you can run scripts by placing them in a directory called cgi-bin in your public_html directory and running them at http://www.cs.virginia.edu/cgi-bin/cgiwrap/yourusername/scriptname. Be VERY careful when designing your scripts - they run on the webserver as you, so don't allow them the opportunity to do anything you wouldn't do! We also recommend that you debug your CGI scripts at http://www.cs.virginia.edu/cgi-bin/cgiwrapd/yourusername/scriptname.