add_action( 'widgets_init', 'create_new_widget' );
function create_new_widget()
{
register_sidebar( array(
'name' => __( 'Custom Sidebar', 'theme-slug' ),
'id' => 'custom_sidebar',
'description' => __( 'Your widget description here', 'theme-slug' ),
) );
}
After that you can call this sidebar by following code. Wherever you want add the following code in that particular place.

dynamic_sidebar( 'left-sidebar' );