Create page and content

Hello,
I’am a beginer in plugin développement, and i am trying to create a page with an form inside…
I create a class in which i use wp_insert_post and it is ok, but now, i don’t know how(or where!?) should i write code for my form…
This class is instancied from admin menu.

That’s an extract of code:

<?php
class register_page
{
	private $id_page;

	public function __construct()
	{
		//Cree une page
		$my_post = array(
				'post_title'    => 'Inscription Individuelle Generee',
				'post_content'  => 'This is my Page.',
				'post_type'		=> 'page',
				'post_status'   => 'publish',
				'post_author'   => 1,
		);

		// Insert the post into the database
		$id_page = wp_insert_post( $my_post );

		//
		//add_action('the_post', array($this,'register_page_construct'));
		add_filter('publish_post', array($this,'register_page_construct'));

		// write in table a log to controle this code is active
		include_once plugin_dir_path( __FILE__ ).'/sql_tool.php';
		$sqlTool = new sql_tool();
		$sqlTool->debug_log("creation de la page");

	}

	public function register_page_construct($content)
	{
//		if ( is_page ($id_page) )
//		{
			echo "<h1>COUCOU</h1>";

		    //write in table a log to controle this code is active
			include_once plugin_dir_path( __FILE__ ).'/sql_tool.php';
			$sqlTool = new sql_tool();
			$sqlTool->debug_log("page_chargee");
//		}
	}

}
?>

Please help me!
Thanks,
Sebastien