Wordpress function add_meta_box() Sample https://9iphp.com/opensystem/wordpress/769.html

functions.php

<?php 
$new_meta_boxes =      
    array(      
        "description" => array(      
            "name" => "description",      
            "std" => "",      
            "title" => "description:"),      
 
        "keywords" => array(      
            "name" => "keywords",      
            "std" => "",      
            "title" => "keywords:")      
    );

function new_meta_boxes() {      
            global $post, $new_meta_boxes;      
            foreach($new_meta_boxes as $meta_box) {      
                $meta_box_value = get_post_meta($post->ID, $meta_box['name'].'_value', true);      
                if($meta_box_value == "")      
                    $meta_box_value = $meta_box['std'];      
                echo'<input type="hidden" name="'.$meta_box['name'].'_noncename" id="'.$meta_box['name'].'_noncename" value="'.wp_create_nonce( plugin_basename(__FILE__) ).'" />';      
                echo'<h4>'.$meta_box['title'].'</h4>';      
                echo '<textarea cols="60" rows="3" name="'.$meta_box['name'].'_value">'.$meta_box_value.'</textarea><br />';      
            }      
        }
function create_meta_box() {      
    global $theme_name;      
    if ( function_exists('add_meta_box') ) {      
        add_meta_box( 'new-meta-boxes', 'new meta box', 'new_meta_boxes', 'post', 'normal', 'high' );      
    }      
}
   function save_postdata( $post_id ) {      
        global $post, $new_meta_boxes;      
        foreach($new_meta_boxes as $meta_box) {      
            if ( !wp_verify_nonce( $_POST[$meta_box['name'].'_noncename'], plugin_basename(__FILE__) ))  {      
                return $post_id;      
            }      
            if ( 'page' == $_POST['post_type'] ) {      
                if ( !current_user_can( 'edit_page', $post_id ))      
                    return $post_id;      
            }       
            else {      
                if ( !current_user_can( 'edit_post', $post_id ))      
                    return $post_id;      
            }      
            $data = $_POST[$meta_box['name'].'_value'];      
 
            if(get_post_meta($post_id, $meta_box['name'].'_value') == "")      
                add_post_meta($post_id, $meta_box['name'].'_value', $data, true);      
            elseif($data != get_post_meta($post_id, $meta_box['name'].'_value', true))      
                update_post_meta($post_id, $meta_box['name'].'_value', $data);      
            elseif($data == "")      
                delete_post_meta($post_id, $meta_box['name'].'_value', get_post_meta($post_id, $meta_box['name'].'_value', true));      
        }      
    }
add_action('admin_menu', 'create_meta_box');      
add_action('save_post', 'save_postdata');
?>

single.php

<?php echo $description = get_post_meta($post->ID, "description_value", true); ?>      
<?php echo $keywords = get_post_meta($post->ID, "keywords_value", true); ?>