on the confirm page, you would need to add the eCart Store Order Summary behavior to store the billing information to an Orders table, and the eCart Store Order Details to store the cart line items to the OrderDetails table.
In the store oder summary behavior, set the Key Column to the primary Key column of the Orders table, and make note of the name of the session that will be created.
In the orderdetails table you should have an orderdetailID column that is used to create the relationship between order and orderdetails.
in the store order details behavior, set the key column to the orderdetailID column and bind that column to the session created by the store order summary behavior.