module

1.create a folder in sites/all/ , and save the folder as “modules”.

2.function naming conventions http://drupal.org/node/206762

3.

A quick note on function naming conventions in Drupal: If you are creating a function that you intend to be strictly private (i.e. no other module should rely on it being a stable function or call it), start the function name with “_your_module_name_”. If your function is public (i.e. it would be OK for another module to call it, and you don’t intend to change its argument signature or behavior often), start the function name with “your_module_name_”. If you are implementing a Drupal hook, you must always name the function “your_module_name_hookname”. Likewise, if you are not implementing a Drupal hook, check the hooks to be sure you have not accidentally picked a function name matching a hook.

http://drupal.org/node/206762

4.http://api.drupal.org/api/drupal/developer–examples–page_example–page_example.module/6