WP Dashboard Widget

wp_dashboard_widget.php

<?php

// https://generatewp.com/introducing-dashboard-widgets-generator/

class Hello_World_Dashboard_Widget {

	public function __construct() {

		add_action( 'wp_dashboard_setup', array( $this, 'add_dashboard_widget' ) );

	}

	public function add_dashboard_widget() {

		wp_add_dashboard_widget(
			'hello_world_widget',
			__( 'Hello World', 'text_domain' ),
			array( $this, 'render_dashboard_widget' )
		);

	}

	public function render_dashboard_widget() {
		echo "Hello World...";
	}

}

new Hello_World_Dashboard_Widget;