How to Make a Sub-theme?

Hi,

Sorry but yes, I'm a newb and this is a newb question. But Drupal rocks and I love it! :)

Again, a question regarding my site at: http://phoenix.appdev.spritle.us

There are two, maybe three sub-templates I need to create. You can see examples of them here: http://phoenix.atomicspacelab.com/news/

I've done much searching, watched many tutorials on sub-themes but I can't get it to work.

My theme is not based upon any pre-built theme. It's just plain standards-compliant XHTML & CSS. From what I've read, this should not be a problem. That said, I've perused other themes and noticed a file called "node.tpl.php", for example:

<?php
// $Id: node.tpl.php,v 1.7 2007/08/07 08:39:36 goba Exp $
?>
  <div class="node<?php if ($sticky) { print " sticky"; } ?><?php if (!$status) { print " node-unpublished"; } ?>">
    <?php if ($picture) {
      print $picture;
    }?>
    <?php if ($page == 0) { ?><h2 class="title"><a href="<?php print $node_url?>"><?php print $title?></a></h2><?php }; ?>
    <span class="submitted"><?php print $submitted?></span>
    <div class="taxonomy"><?php print $terms?></div>
    <div class="content"><?php print $content?></div>
    <?php if ($links) { ?><div class="links">&raquo; <?php print $links?></div><?php }; ?>
  </div>

I feel bad for asking, given all the very-well written documentation available, but after three days of trying on my own I'm feeling stumped.

Thanks for your help!

Regards,

Tofu