Examples for Developers
http://drupal.org/project/examples

This set of modules is intended to provide small working examples of Drupal's
features and APIs.  The modules strive to be simple, well documented and
modification friendly to help developers quickly learn their inner workings,
with a little reading and hands on experience.

You can have a quick glimpse at the current Examples in the demo site: 
http://d7.drupalexamples.info/

Suggestions, corrections and new examples are welcome.  Don't be shy if you're
just starting, as precisely because of that you will know the questions and
problems of a newcomer better than a seasoned developer!

Setup

1. Install Examples for Developers (unpacking it to your Drupal
   sites/all/modules directory if you're isntalling by hand, for example).
2. Enable any Example modules in Admin menu > Site building > Modules.
3. Rebuild access permissions if you are prompted to.
4. Profit!  The examples will appear in your Navigation menu (on the left
   sidebar by default; you'll need to reenable it if you removed it).

Now you can read the code and it's comments and see the result, experiment with
it, and hopefully quickly grasp it's working.

If you find a problem, incorrect comment, obsolete or improper code or such,
please let us know by creating a new issue at
http://drupal.org/project/issues/examples