I made a my own theme to WordPress and Admin Menu missing from frontend

First of all, you should keep the below code in your theme( header.php file ).

   <?php wp_head(); ?>

Something looks likes the below in header.php file

<!doctype html>
<html <?php language_attributes(); ?>>
<head>
<meta charset="<?php bloginfo( 'charset' ); ?>">
<meta name="viewport" content="width=device-width, initial-scale=1">
<?php wp_head(); ?>
</head>

Lastly, You need to put the following code in your footer.php, before closing tag

  <?php wp_footer(); ?>

The code looks like these

   <?php wp_footer(); ?>
   </body>
</html>