Service PO with BAPI_PO_CREATE1

Hi All,

Kindly explain me how to create service PO with BAPI_PO_CREATE1 where I need to pass,

G/L account and CostCenter .

I searched previous links, but i didnt understand , why to maintain two entries in POSERVICE .

And also tell me how to give that  "Package numbers and , Sub Package numbers, Line numbers , Serial  line ,Serial numbers

for multiple values when i need to update from flat file.

Regards,

Gopichand.