It's actually a misunderstanding (English is not my mother-tongue 
)
I am looking for a simple way to create the function to post 1Header and its nItems to my custom Header and Item tables.
Yeah, the example code uses the BAPI_SALESORDER_CREATEFROMDAT2 but, since I'm in a trial version of SAP NW ABAP 7.40, No ECC Data exists...
Thought there would be other examples of Header-Item "creation-modules" that I could implement for my custom tables.
I'm trying to invent the wheel again on purpose, in order to really grasp the subject, knowing that in a customer project, Function Modules will already be in place for most of our desired OData actions.