Default order type, in ovlk

Dear sd gurus good mng have a nice day

i have one doubt in OVLK delivery document type control in ORDER REFERENCE tab 2 Field are available

1 . Order Required : it tells that has no reference document to an existing sales order is allowed

ex sales order required

no proceeding documents required

2. Default order type:it tells when you create sales order don't refer to existing orders we must provide some of the control criteria normally copied from header document into the delivery document

pl could explain a little bit more bz a strike out point i need to understand exactly . pl give one example

thank you so much for your cooperation ...