Wordpress plugin development

Hi friends this is my very first tutorial in wordpress plugin development. In this tutorial we are going to create an login/logout widget as a plugin.
step 1:
Create a folder in wp-content/plugins/ and name it as whatever u want. But it should represent your plugin name, here i'm going to create an folder ' ktm-wp-login '. Now the folder will be in wp-content/plugins/ktm-wp-login.
step 2:
Create a file ktm-wp-login.php inside the ktm-wp-login folder and write the following code on it.

/*
Plugin Name: ktm Wordpress Login
Description: With this plugin we can login or logout. 
Author:Karthi
Version:1.0
Author URI:http://techpointt.wordpress.com
Plugin URI:http://techpointt.wordpress.com
*/

step 3:
For creating this plugin we need the following functions and hooks:
-wp_loginout()
-wp_register()
-register_widget()
and an action ' widgets_init '

Lets start,
In order to register our widget we need a function register_widget()

<?php
add_action('widgets_init','ktm_register_widget');

function ktm_register_widget(){
    register_widget('ktm_login_widget');
}
//Check whether the class is already exist or not.
if(!class_exists('ktm_login_widget')){

 //Extend our class with core class WP_Widget
 class ktm_login_widget extends WP_Widget{

 //Initializing the widget with constructor function
  function ktm_login_widget(){
    $widget_opts = array(
     'classname' => 'ktm_login_widget', //class name for our widget
     'description'=>'login/logout' //description will be shown in dashboard active widget's box
    );
    //Wp_Widget('id_for_our_widget','title_for_our_widget_in_dashboard','options')
    $this->WP_Widget('ktm_login_widget_id','Log-in/Log-out',$widget_opts);
  }

  //the parameter $instance used to save data in wp_options table
  /*WP_Widget is a core class uses 3 functions 
    Form()   -to show form after we enable it in sidebar widget 
    Update() -to update new data entered by us.
    Widget() -front end widget content.*/
 function form($instance){
   //Initializing for the first time
   $defaults = array('title'=>'widget title');
   //Parse the value with incoming args
   $instance = wp_parse_args( (array) $instance, $defaults);
   $title = $instance['title'];
   //get_field_name() helps to fetch encoded data from wp_options table. We can find the value in ktm_login_widget_id    name

   echo 'Title: ';

 }

 function update($new_instance,$old_instance){
   $instance = $old_instance;
   $instance['title'] = strip_tags($new_instance['title']);
   return $instance;
 }

 function widget($args, $instance){
   if(is_user_logged_in()){
     global $current_user;
     $user = $current_user->user_login;
   }else{
     $user = 'Guest';
   }
   echo $args['before_widget'];
   echo $args['before_title'].$instance['title'].' '.$user.$args['after_title'];
   echo "
     <ul>
	<li>".wp_loginout(get_permalink(),true)."</li>
	<li>".wp_register()."</li>
     </ul>";
   echo $args['after_widget'];
  }
 }
}
?>

You can download this plugin as .doc format.

To know more about writing plugin visit codex Writing a plugin page