How to add multiple custom widget areas

You have to register multiple areas:

function new_sidebar_widget_init() {
   register_sidebar( array(
        'name' => 'new-sidebar',
        'id' => 'new-sidebar',
        'before_widget' => '<div id="new-sidebar">',
        'after_widget' => '</div>',
        'before_title' => '',
        'after_title' => '',
    ) );
    register_sidebar( array(
        'name' => 'new-sidebar-1',
        'id' => 'new-sidebar-1',
        'before_widget' => '<div id="new-sidebar">',
        'after_widget' => '</div>',
        'before_title' => '',
        'after_title' => '',
    ) );
}
add_action( 'widgets_init', 'new_sidebar_widget_init' ); 

And then you can use them based on their ID:

<?php  dynamic_sidebar( 'new-sidebar' ); ?> 

<?php  dynamic_sidebar( 'new-sidebar-1' ); ?>