Woocommerce custom hooks

Hi everybody,

I’m trying to add custom fields into my VW Kids Theme but nothing happen ??

I try several Hooks lik this :

add_action( 'woocommerce_before_checkout_form', 'ts_checkout_before_customer_detaildds', 10 );

function ts_checkout_before_customer_detaildds(){
echo 'woocommerce_checkout_before_customer_details woocommerce_before_checkout_form ';
}

Can anyone help me with this ?