WordPress - Add dynamic sidebar

functions.php

<?php
add_action( 'init', 'theme_widgets_init' );
function theme_widgets_init() {
    register_sidebar( array (
    'name' => 'Widget',
    'id' => 'primary_widget_area',
    'before_widget' => '<div id="%1$s" class="widget-container %2$s">',
    'after_widget' => "</div>",
    'before_title' => '<h3 class="widget-title">',
    'after_title' => '</h3>',
    ) );
}

index.php

<?php dynamic_sidebar('primary_widget_area'); ?>