woocommerce_form_field('myName', array(
    'type' =>'text',
    'class'=>array('my-field-class form-row-wide'),
    'label'=>__('First Name'),
    'placeholder'=>__('Please enter your name'),
), $checkout->get_value('myName'));

/*Update the info with the checkout*/
add_action('woocommerce_checkout_field_update_order_meta','my_custom_checkout_field_update_meta');
function my_custom_checkout_field_update_meta($order_id){
    if($_POST['MyName'])
        update_post_meta($order_id, 'First Name',esc_attr($POST['MyName']));
}