Adding theme support

The help page at https://wpjobmanager.com/document/enabling-full-template-support/ is pretty vague about how to do this. I am totally new to playing around with theme support.

I am assuming that “add_theme_support( ‘job-manager-templates’ );” would go in the theme’s or child theme’s functions.php? How is this called? WordPress page for adding theme support https://codex.wordpress.org/Function_Reference/add_theme_support mentions this code:
function custom_theme_setup() {
add_theme_support( ‘job-manager-templates’ );
}
add_action( ‘after_setup_theme’, ‘custom_theme_setup’ );

Is this what I have created above what I would need to do this? Would ‘after_setup_theme’ be ‘init’ instead? Or do I not need any of the code and just “add_theme_support( ‘job-manager-templates’ );”?

Also, how can I know that this has worked?

Thanks!

https://wordpress.org/plugins/wp-job-manager/