How to build a wordpress plugin?

Page
    Create an image in all posts

Create a folder in D:\wamp\www\mywork\wp-content\plugins\addimage

Create a file named as addimage.php

<?php
/*
* Plugin Name:Add Image
* Version:1.0
* Author:Nithin Thomas
* Author Url:http://nithinthomasblog.wordpress.com
* Description:Powerful plugin with adding images to post
*/

function addImage($post)
{
$image="“;
$image.=$post;
return $image;
}
add_filter(“the_content”,”addImage”);

?>