how to make simple plugin in wordpress

Overview

how to make basic helloworld plugin in wordpress
how to add custom menu in wordpress admin panel
how to use hooks in wordpress
how to set_option works in wordpress plugin
how to show get_option values in frontend with wp_footer hook
how to make sub menu and menu pages in admin panel
this video has answers of all these above’s questions.

Code Snippet

<?php
add_action('admin_menu', 'my_admin_menu');

function my_admin_menu () {
	//parameters details
	 //add_management_page( $page_title, $menu_title, $capability,
 $menu_slug, $function );
	 //add a new setting page udner setting menu
  //add_management_page('Footer Text', 'Footer Text', 'manage_options',
 __FILE__, //'footer_text_admin_page');
  //add new menu and its sub menu 
  add_menu_page('Footer Text title', 'Footer Settings', 'manage_options',
 'footer_setting_page', 'footer_text_admin_page');
add_submenu_page( 'footer_setting_page', 'Page title', 'Sub-menu title', 
'manage_options', 'child-submenu-handle', 'my_magic_function');
}

function footer_text_admin_page () {
  echo 'this is where we will edit the variable';
}

// mt_settings_page() displays the page content for the Test Settings submenu
function mt_settings_page() {
    echo "<h2>" . __( 'Footer Settings Configurations', 'menu-test' ) . "</h2>";
	include_once('footer_settings_page.php');
}
?>
<?php
    global $chk;
    if(isset($_POST['wphw_submit'])){
            wphw_opt();
    }
    function wphw_opt(){
        $hellotxt = $_POST['footertextname'];
        global $chk;
        if( get_option('footer_text') != trim($hellotxt)){
            $chk = update_option( 'footer_text', trim($hellotxt));
        }
    }
?>
<div class="wrap">
  <div id="icon-options-general" class="icon32"> <br>
  </div>
  <h2>Footer Settings</h2>
  <?php if(isset($_POST['wphw_submit']) && $chk):?>
  <div id="message" class="updated below-h2">
    <p>Content updated successfully</p>
  </div>
  <?php endif;?>
  <div class="metabox-holder">
    <div class="postbox">
      <h3><strong>Enter footer text and click on save button.</strong></h3>
      <form method="post" action="">
        <table class="form-table">
          <tr>
            <th scope="row">Footer Text</th>
            <td><input type="text" name="footertextname" 
value="<?php echo get_option('footer_text');?>" style="width:350px;" /></td>
          </tr>
          <tr>
            <th scope="row">&nbsp;</th>
            <td style="padding-top:10px;  padding-bottom:10px;">
<input type="submit" name="wphw_submit" value="Save changes" class="button-primary" />
</td>
          </tr>
        </table>
      </form>
    </div>
  </div>
</div>

<?php
function your_function() {
   echo "<div style='color: red;
    font-size: 30px;
    margin: 20px;'>".get_option('footer_text')."</div>";
}
add_action( 'wp_footer', 'your_function' );
?>

 

Summary

basic helloworld plugin in wordpress,how to add custom menu in wordpress admin dashboard,hooks in wordpress,use of set_option and get_option in wordpress