How can I send to the administrator, the user's...

How can I send to the administrator, the user's credentials with a note HIKASHOP_USER_DETAILS, ordering that it specifies for registration.
For example.
Fields of type user, the user has formed an order.
In the mail message to the administrator to come to his order, and all the data which he pointed out at registration.

You will have to edit the email order admin notification via the menu System->Emails (business edition).
Displaying a custom user field there is quite easy. You can do at the end like that:

my field:<?php echo $data->customer->COLUMN_NAME; ?>

where COLUMN_NAME is the column name of the custom field.