Create Category when user registers

I’m working on a project where i need to create category automatically everytime when new user registers.. I dont want to get plugin for this.

What i have come up with in themes functions.php is this:

function kn_create_category() {
wp_create_category('example name');
}
add_action( 'user_register', 'kn_create_category' );

Now: How can i get the just registered users ID to be category name?

And please, simple anwser’s i’m WP newbie ?? Thanks!