create a wp plugin

<?php 
/*
 * Plugin Name: Custom-Plugin
 * Plugin URI: 
 * Description: Test Page. 
 * Version: 0.0.1
 * Author:
 * Author URI: 
 */

add_action('admin_menu', 'function_create_menu');
// Create WordPress admin menu
function function_create_menu(){

//The icon in Base64 format
$icon_base64 = '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';

//The icon in the data URI scheme
$icon_data_uri = 'data:image/svg+xml;base64,' . $icon_base64;

$page_title = 'Hello World';
$menu_title = 'My Admin Menu';
$icon_data_uri;
$position   = '20';
$capability = 'manage_options';
$menu_slug  = 'newPage';
$function   = 'test_page';

add_menu_page(
    $page_title,
    $menu_title,
    $capability,
    $menu_slug,
    $function,
    $icon_data_uri,
    $position
);

}

// Create WordPress plugin page
function test_page()
{
?>
<h1>WordPress test site</h1>

<?php
}

?>