What went wrong? my plugin

<?php
/*
Plugin Name:My Plugin
*/

function my_function($text){
	if(isset($_POST["name"])) {
		$name = $_POST['name'];
	} else {
		echo "
			<form method='post' action='options.php'>
			name : <input type='text' name='name'>
			<input type='submit' value='submit'>
			</form>
		";
	}

	$text = str_replace('foo',$name,$text); //replace $name -> foo
	return $text;
}

add_filter('the_content','my_function');
?>

==========================================================
path : /wp-content/plugins/myplugin/options.php

1. <form method=’post’ action=’options.php’>

result = Object not found!

or

2. <form method=’post’ action=’wp-content/plugins/myplugin/options.php’>

result = Fatal error: Call to undefined function add_filter() in D:\xampp\htdocs\thwordpress\wp-content\plugins\myplugin\options.php on line 23
======================================================================