Create WordPress Custom Admin Pages

function my_admin_menu() {
	add_menu_page(
		__( 'Sample page', 'my-textdomain' ),
		__( 'Sample menu', 'my-textdomain' ),
		'manage_options',
		'sample-page',
		'my_admin_page_contents',
		'dashicons-schedule',
		3
	);
}

add_action( 'admin_menu', 'my_admin_menu' );


function my_admin_page_contents() {
	?>
		<h1>
			<?php esc_html_e( 'Welcome to my custom admin page.', 'my-plugin-textdomain' ); ?>
		</h1>
	<?php
}