I can't get my custom widget area to show on my WordPress site

I can’t get my sidebar to appear on my site.
I add a widget section since there wasn’t any:
function.php

<?php
if (function_exists('register_sidebar'))
    // Area 1
  register_sidebar( array (
  'name' => 'Primary Widget Area',
  'id' => 'primary_widget_area',
  'before_widget' => '<li id="%1$s" class="widget-container %2$s">',
  'after_widget' => "</li>",
    'before_title' => '<h3 class="widget-title">',
    'after_title' => '</h3>',
  ) );

    // Area 2
  register_sidebar( array (
  'name' => 'Secondary Widget Area',
  'id' => 'secondary_widget_area',
  'before_widget' => '<li id="%1$s" class="widget-container %2$s">',
  'after_widget' => "</li>",
    'before_title' => '<h3 class="widget-title">',
    'after_title' => '</h3>',
  ) );

    // Footer
  register_sidebar( array (
  'name' => 'Footer',
  'id' => 'footer_widget_area',
  'before_widget' => '<li id="%1$s" class="widget-container %2$s">',
  'after_widget' => "</li>",
    'before_title' => '<h3 class="widget-title">',
    'after_title' => '</h3>',
  ) );
?>

sidebar.php

<?php dynamic_sidebar( 'sidebar-3' );  ?>

I’m following this tutorial: WordPress Widgets Tutorial
And I’ve tried many online examples and here are two: wordpress custom modules/widget areas on the page? can i make my own? and Widgetizing Themes

Solutions Collecting From Web of "I can't get my custom widget area to show on my WordPress site"

Your have created three sidebars and that are primary_widget_area, secondary_widget_area, footer_widget_area

But in the sidebar, you call a different sidebar name sidebar-3; that’s why your sidebars are not displaying.

Try the following code in sidebar.php:

// To display primary_widget_area sidebar
<?php if ( is_active_sidebar( 'primary_widget_area' ) ) : ?>
    <?php dynamic_sidebar( 'primary_widget_area' ); ?>
<?php endif; ?>

// To display secondary_widget_areasidebar
<?php if ( is_active_sidebar( 'secondary_widget_area' ) ) : ?>
    <?php dynamic_sidebar( 'secondary_widget_area' ); ?>
<?php endif; ?>

// To display footer_widget_areasidebar
<?php if ( is_active_sidebar( 'footer_widget_area' ) ) : ?>
    <?php dynamic_sidebar( 'footer_widget_area' ); ?>
<?php endif; ?>

Thank you!