Example of dashboard widget for WordPress.

dashboard-widget.php

<?php
/**
 * Dashboard widget
 *
 * @package WordPress
 * @version 1.0.0
 * @author Denis Žoljom <denis.zoljom@gmail.com>
 * @license GNU General Public License v2 or later
 * @link http://madebydenis.com/
 * @since  1.0.0
 */

/********* Add More Dashboard Widget ***********/
add_action( 'wp_dashboard_setup', 'utter_add_dashboard_widgets' );

if ( ! function_exists( 'utter_add_dashboard_widgets' ) ) {
	/**
	 * Add Dashboard Widgets
	 *
	 * @since 1.0.0
	 */
	function utter_add_dashboard_widgets() {
		wp_add_dashboard_widget( 'dashboard_widget', esc_html__( 'Utter Addons','utter' ), 'utter_additional_addons' );
	}
}

if ( ! function_exists( 'utter_additional_addons' ) ) {
	/**
	 * Utter Additional addons
	 *
	 * @return void                Dashboard widget HTML.
	 */
	function utter_additional_addons() {
		?>
		<div class="most_read">
			ADD WIDGET IFRAME
		</div>
		<?php
	}
}