Keep in mind that those themes have been created to address the needs of many people. The themes must be able to handle all kinds of scenarios, which means they have been designed to allow you to dynamically add various columns and other layout elements, and to support custom theming for features and modules which you might not even need. These themes usually include a large amount of PHP code that essentially says, "If this setting is true, then show this part this way, or else show that." This makes the theme very flexible, but also very complicated.
However, your theme doesn't need to work for everyone. It only needs to do the things your site requires and nothing more. All that you need are a few bits of PHP, which you can simply copy and paste into your own HTML template. These PHP snippets tell Drupal to load its dynamic content in those spots.
You might also find it useful to have a look at Drupal's "most basic" core template files (those used when a theme doesn't provide any alternative template files to override them). To view these basic templates, look in the /modules/system folder of your Drupal installation (in particular, look at page.tpl.php and node.tpl.php).
Just a few simple & basic elements make up a Drupal theme
The "main" template file in Drupal is called page.tpl.php. Make a copy of your website layout/template and call it page.tpl.php. Then, simply paste the following bits of code into your layout, in the locations noted (all the code mentioned in this lesson goes in thepage.tpl.php file).
Starting your page
If you're using Drupal 5:
<html xmlns="http://www.w3.org/1999/xhtml" lang="<?php print $language ?>" xml:lang="<?php print $language ?>">
If you're using Drupal 6:
<html xmlns="http://www.w3.org/1999/xhtml" lang="<?php print $language->language ?>" xml:lang="<?php print $language->language ?>" dir="<?php print $language->dir ?>">
This is the recommended way to start your page, rather than just using <html>. The extra definitions here aid in proper validation and language handling of the resulting HTML markup.
The <head> section of your site
<head>
<title><?php print $head_title; ?></title>
<?php print $head; ?>
<?php print $styles; ?>
<?php print $scripts; ?>
</head>
The side bars or columns of your layout
Most websites have a left and/or right column next to the "main" larger content area. These side bars usually contain various features and information (for instance a log-in form, navigation, recent comments, etc). In Drupal these features/information are called "Blocks", and you can customize where they show up on your page by going to Administer > Site building > Blocks (admin/build/block). In order for Drupal to know where to put the Blocks though, you need to add some "placeholders" to your theme (Drupal calls these placeholders "Regions"). There are more of these placeholders available (and you can create your own custom ones too) but it's important to add the side bar one(s) at first, since the admin menu appears in them. Add the below Region(s) to your side bar:
If you're using Drupal 5:
<?php print $sidebar_left; ?>
...and/or...
<?php print $sidebar_right; ?>
If you're using Drupal 6:
<?php print $left; ?>
...and/or...
<?php print $right; ?>
Menu system / navigation
Drupal's default menu for your site's content is called Primary Links. There is also aSecondary Links menu which can show related sub-pages under the Primary menu. When stripped of all images and styles, a menu in Drupal is nothing more than a nested unordered list, in plain HTML, with links for each list item. You can use CSS to style a menu in any way you want; changing how it looks, whether it is horizontal (like tabs) or vertical, etc.
To make the Primary and Secondary Links menus appear on your site, paste the following into either the top area of your theme (for instance, if your menu is going to be styled as tabs or buttons), or in the sidebar area (for instance if you plan to have your menu show vertically in the sidebar).
Simple way:
Here's the simple version to use, if you're already sure you want to use "both" Primary and Secondary Links (or feel free to delete the Secondary Links portion if you don't need it):
<div id="primary">
<?php print theme('links', $primary_links); ?>
</div> <!-- /#primary -->
<div id="secondary">
<?php print theme('links', $secondary_links); ?>
</div> <!-- /#secondary -->
More flexible way:
If you're not sure that you will have both Primary and Secondary Links, you could use the following code instead (it's the same, but just does a "check" to see if the menus are enabled, and only shows them if they are):
<?php if ($primary_links): ?>
<div id="primary">
<?php print theme('links', $primary_links); ?>
</div> <!-- /#primary -->
<?php endif; ?>
<?php if ($secondary_links): ?>
<div id="secondary">
<?php print theme('links', $secondary_links); ?>
</div> <!-- /#secondary -->
<?php endif; ?>
The main "dynamic" content of the page
At this point, you've added all of the "framework" of your site's layout which surrounds every page, and is generally similar or the same throughout the entire site. Now though, it's time to include the area where actual Content will be displayed in the template (different content depending on the page being viewed, of course).
Simply locate the spot in your template where the main content is to be displayed (usually the center of the page, after the header and between any sidebars), and paste the below code in that spot (if you'd like to re-order things feel free, but otherwise you can simply paste this as-is):
<?php print $breadcrumb; ?>
<?php if ($mission): ?><div id="mission"><?php print $mission; ?></div><?php endif; ?>
<div id="content">
<?php if ($title): ?><h1 class="title"><?php print $title; ?></h1><?php endif; ?>
<?php if ($tabs): ?><div class="tabs"><?php print $tabs; ?></div><?php endif; ?>
<?php if ($show_messages): print $messages; endif; ?>
<?php print $help; ?>
<?php print $content; ?>
</div>
Footer: Add footer and footer message
To add a footer region and the footer message you have set in the administration backend you can use:
<?php if ($footer_message || $footer) : ?>
<div id="footer-message">
<?php print $footer_message . $footer;?>
</div>
<?php endif; ?>
Add a final tag at the bottom of your theme
Paste the following at the end of your page.tpl.php file. You must have this tag at the bottom, which will dynamically include any scripts that need to appear at the bottom of the page, as well as close up any loose ends and tags that might have been left open:
<?php print $closure; ?>
</body>
</html>
For Drupal 6: Create a YourThemeName.info file
Lastly, in Drupal 6, the one final element is to create a YourThemeName.info file (whereYourThemeName is the name of your theme, with no spaces). Simply make a blank file and paste the following code into it, customize it with the appropriate name/description, and save it in the same directory along with the rest of your theme's template files:
name = YourThemeName
description = Description of YourTheme
core = 6.x
engine = phptemplate
stylesheets[all][] = style.css
regions[left] = Left sidebar
regions[right] = Right sidebar
regions[content] = Content
regions[header] = Header
regions[footer] = Footer
The "regions" portion after style.css includes all of Drupal's "standard" regions, and is recommended so that you can easily remove regions you don't want to use, or add custom regions. If you want to add custom regions, you must manually include any of the default ones you wish to keep as well or the defaults will disappear from your theme (simply copy/paste them from this page or another theme). If you want to add a custom region, simply copy one of the region lines and rename it.
That's all - Paste the above bits of code into ANY site layout or template, and you have a basic, functional Drupal theme.