If you want a meta box, this will do it. It'll be up to you what you want to put in it and how each field is saved / rendered.

This example was adapted from add_meta_box.

if ( is_admin() ) {
    add_action( 'load-post.php', 'BoxPost::init' );
    add_action( 'load-post-new.php', 'BoxPost::init' );
}

if( ! class_exists('BoxPost')) :
/**
 * The Class.
 */
class BoxPost {

  const SLUG = "boxpost_meta_box_name";
  const NONCE_SLUG = "boxpost_inner_custom_box";
  const NONCE = "boxpost_inner_custom_box_nonce";
  const TEXT_DOMAIN = 'text_domain';

    /**
     * Hook into the appropriate actions when the class is constructed.
     */
    static public function init() {
        add_action( 'add_meta_boxes', 'BoxPost::add_meta_box' );
        add_action( 'save_post', 'BoxPost::save' );
    }

    /**
     * Adds the meta box container.
     */
    static public function add_meta_box( $post_type ) {
        $post_types = array('post', 'page');   //limit meta box to certain post types
        if ( in_array( $post_type, $post_types )) {
            add_meta_box(
                  self::SLUG
                , __( 'BoxPost Headline', self::TEXT_DOMAIN )
                , 'BoxPost::render_meta_box_content'
                , $post_type
                , 'advanced'
                , 'high' // 'high', 'core', 'default' or 'low'
            );
        }
    }

    /**
     * Save the meta when the post is saved.
     *
     * @param int $post_id The ID of the post being saved.
     */
    static public function save( $post_id ) {

        /*
         * We need to verify this came from the our screen and with proper authorization,
         * because save_post can be triggered at other times.
         */

        // Check if our nonce is set.
        if ( ! isset( $_POST[ self::NONCE ] ) )
            return $post_id;

        $nonce = $_POST[ self::NONCE  ];

        // Verify that the nonce is valid.
        if ( ! wp_verify_nonce( $nonce, self::NONCE_SLUG ) )
            return $post_id;

        // If this is an autosave, our form has not been submitted,
        // so we don't want to do anything.
        if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
            return $post_id;

        // Check the user's permissions.
        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;
        }

        /* OK, its safe for us to save the data now. */

        // Sanitize the user input.
        $mydata = sanitize_text_field( $_POST['boxpost_meta_field'] );

        // Update the meta field.
        update_post_meta( $post_id, '_boxpost_meta_field_value_key', $mydata );
    }


    /**
     * Render Meta Box content.
     *
     * @param WP_Post $post The post object.
     */
    static public function render_meta_box_content( $post ) {

        // Add an nonce field so we can check for it later.
        wp_nonce_field( self::NONCE_SLUG, self::NONCE  );

        // Use get_post_meta to retrieve an existing value from the database.
        $value = get_post_meta( $post->ID, '_boxpost_meta_field_value_key', true );

        // Display the form, using the current value.
        echo '<label for="boxpost_meta_field">';
        _e( 'Description for this field', self::TEXT_DOMAIN );
        echo '</label> ';
        echo '<input type="text" id="boxpost_meta_field" name="boxpost_meta_field"';
        echo ' value="' . esc_attr( $value ) . '" size="25" />';
    }
}

endif; //BoxPost