Example: node_example.module
The following entry in the API provides code for this example. Comments sprinkled throughout should provide guidance in understanding what is going on here, and in the steps you should take if you are trying to implement something similar.
node_example.module | Drupal API
Note: the "source" link on that page is broken, so after reading the module description, go here for the actual code:
(click "view" or "download" from those links for the actual source code.)