eCart cart summary

I cant figure out the relationship between the database tables 'orders' and 'orderDetails'
However I want to record the first name, last name, email and ItemName in the database, orders table.
// WA eCart Store Cart Summary in Db in the confirm page.
$WA_table = "orders";
In the orders table I have created 4 new fields for 'first name', 'last name', 'email' and 'ItemName'.
I Have opened eCart Store Cart Summary in Db (orders Table) from the Server Behaviours panel
The new fields in the table now appear, I have dynamically linked them to the checkout form details in the ecart checkout form
"<?php echo ((isset($_POST["firstname"]))?$_POST["firstname"]:""); ?>"
And saved. All looks ok.
All the inserted items are available in the session.
Is this correct, Do I need to add any other information elsewhere?
Is there another way of doing this?
Thanks
David