Here is one place you can start if you are looking for basic info on creating a plugin:

http://codex.wordpress.org/Writing_a_Plugin

 

Create a file in the plugins folder. Call it whatever you’d like.

 

Place a comment block at the top like this, filling in the info specific to your plugin:

<?php
/*
Plugin Name: My Plugin
Plugin URI: http://blog.kennyray.com
Description: This is a plugin
Version: 1.0
Author: Kenny Ray
Author URI: http://blog.kennyray.com
License: GPL2
*/
?>

At this point, you will see your Plugin in the plugins section of the site admin.

 

WordPress plugins: Where to begin