You can write CGI programs in lots of different languages. Here is a simple one in Perl. If you run this code, it will output HTML. If you save that HTML to a file, you can display that file contents in a browser (use open | file).

#!/usr/bin/perl -w

use strict;
use CGI;

my $q = new CGI;
my $timestamp = localtime;

print $q->header ("text/html"),
      $q->start_html ( -title => "Current Time"),
      $q->h2 ("Current Time"),
      $q->hr,
      $q->p( "This system figures current time as: ",
             $q->b($timestamp)
            ),
      $q->end_html;
[download]

You can call this short thing, say "time". Have your friendly (I hope) web administrator set this up so that it can be accessed via a URL and bingo you have your first CGI program working! Basically to output a web page, write a program that spews out HTML to stdout. There is some config stuff at the server end, but this is the idea of what your program has to do.