how do i develop a global nav and local nav to be wordpress dynamic?

WordPress calls these Navigation Menus. There are a few steps:

1. Set up a child theme, if you aren’t already using one. That way your changes won’t be lost when the main theme is updated.

2. Register the menu – in your child theme’s functions.php file,

function mythemeslug_register_custom_menu() {
register_nav_menu('topnav', __('Top Nav'));
}
add_action('init', 'mythemeslug_register_custom_menu');

3. Call the menu in the theme – you’ll most likely want this in your child theme’s header.php file.

wp_nav_menu(array('menu' => 'topnav'));

There are various ways to call it but in this example you’re calling the menu with the name ‘topnav’. You can alternatively designate a ‘theme location’ and call it that way. You can also control the HTML container and CSS classes, among other things. Follow the links above to learn more about various options.

4. Build the menu in wp-admin – you can do this in either the Customizer or under Appearance > Menus.

If you need to heavily customize the HTML markup, you can create a custom walker.