I don't fully understand the question, but the way it is designed is that if you want to allow people to order a pre-defined product or service, you use an order form, and if you want to allow people to request a quote which requires manual input from the administrator, you use a quote request form.
It sounds like you want to use an order form to create an invoice without first creating an order. This is not currently possible, although if you don't want the client to see the order record, you can just disable the My Orders page (using Website->Display Options).
