Good Theming Tutorial?

I still need to spend some time to learn using devel module. thank you for the information on devel i never thought that it can help creating templates. can you tell me abit more about Devel module?

It's like Firebug for PHPTemplate. That about sums it up :)

If you don't use Firebug yet (I assume you do already), run don't walk to google so you can get it installed in Firefox. It is the single most important tool available for anyone doing HTML/CSS work.

Watch the Theme Devel screencast:
http://drupal.org/node/209561

I have read several PHP tutorials online and right now reading a book "PHP 5 and MySQL Bible" I am starting to understand how PHP generally work but what I need to get the job done now is to understand how phptemplate works in drupal and how to manipulate them...

OK, you shouldn't be too far away from "getting it" then :) You are probably just missing one or two simple pieces that will make the whole puzzle fit together. I not sure exactly which pieces they are though, so I'll give you a quick and rough overview (the Drupal 6 theme guide should fill in the actual details)...

The important common PHP stuff to understand for this is functions - eg how you define them, how to call them, and how to return stuff from them. That will allow you to make more sense of the API docs at http://api.drupal.org

When Drupal (eg core or a module) wants to create some HTML output from some data, it does so via theme functions or templates. These get processed by the theme() function. The theme function then goes looking for the correct theme function or template to use to render that data as HTML and also looks for any overrides in the current theme.

I'll explain overriding theme functions as it sounds like you've already used template overrides...

eg the code in the user module creates a block with lists of users in them, and you want to override that.
The block function is user_block(). If you look through the code you'll see some lines that look like :

<?php
...
      case 2:
        if (user_access('access content')) {
          // Retrieve a list of new users who have subsequently accessed the site successfully.
          $result = db_query_range('SELECT uid, name FROM {users} WHERE status != 0 AND access != 0 ORDER BY created DESC', 0, variable_get('user_block_whois_new_count', 5));
          while ($account = db_fetch_object($result)) {
            $items[] = $account;
          }
          $output = theme('user_list', $items);

          $block['subject'] = t('Who\'s new');
          $block['content'] = $output;
        }
        return $block;
...
?>

Don't worry too much about that - the theming bit to look at in there is: $output = theme('user_list', $items);. This is how Drupal core and modules call the theme layer via the theme() function to render their data.

The theme() function is sent a string identifying the theme 'hook' to use and the data (eg in this case the array $items which came from a database query) to be sent to the theme hook.

If the theme layer doesn't find any overrides for the 'user_list' hook, it will use the default fallback implementation called theme_user_list(). If your template.php has a function called phptemplate_user_list() or yourthemename_user_list() it will use those instead of theme_user_list().

So if you haven't overridden theme_user_list(), $output = theme('user_list', $items); effectively uses $output = theme_user_list($items); which is the default implementation for the HTML output.

This is the default implementation of the 'user_list' theme function (I've added some comments):

<?php
function theme_user_list($users, $title = NULL) {
  if (!empty($users)) {   // checks the list of users isn't empty
    foreach ($users as $user) {   // loops over each user item in the users list
      $items[] = theme('username', $user);   //  appends the themed user name for that user onto a list of items
    }
  }
  return theme('item_list', $items, $title);  // sends the new list of rendered items to be themed as an item list and returns it back to the user module (or other module) to use as the HTML output
}
?>

If you're wondering where the actual HTML is, well you'll notice the data that gets returned from the function also passes through another couple of theme hooks eg 'username' (default function is theme_username()) and 'itemlist' (default function is theme_item_list()). Each of those functions could also be overridden in your theme.

Basically the easiest way to override a theme function is to copy the original function into your themes template.php file and rename it eg yourthemename_item_list. Once you've renamed it, you can alter the PHP code inside your copy of the function.

--
Anton

Theres no point in creating a generic template.php file (for starters as you described) since this is going to be site specific - i.e. to include customisations for your particular site - see styro's very informative post above. That said, one of the handiest things to use in template.php are preprocess funtions - which are covered in some detail in the Drupal 6 theme guide.

"have the Zen theme installed alongside your custom theme"

Zen is a starter theme framework - the idea is to build a subtheme and never touch the core framework. A similar but different framework is Genesis which works the same way (copy/paste the included subtheme to get started sort of thing).

If you want a pretty serious introduction to what you can do in template.php with preprocess functions and other theme function over rides take a look at both Zen and Genesis and a number of other themes that make extensive use of template.php.

Sorry for the delay, I was lacking my laptop for awhile, so I've been disconnected from the internet...

Anyways, after you install the Zen theme, you can check the read me file, or the documentation linked from the project page: http://drupal.org/node/226507

Once the basic steps are complete, number 9 tells you how to where to get the a template.php file to customize within the Zen theme.