add_theme_support('menus');

function register_my_menu() {
  register_nav_menu('header-principal',__( 'Header Principal' ));
}
add_action( 'init', 'register_my_menu' );


<?php
  $args = array(
    'menu' => 'Header Principal',
    'theme_location' => 'header-principal',
    'container' => false
  );
  wp_nav_menu( $args );
?>