BAPI_REQUISITION_CREATE - Parameter EXTENSIONIN

Hello Gurus,

I wonder if someone can help me in how to fill the parameter EXTENSIONIN,

I know a Little bit that I have to concatenate, but I need more information, how I fill the fields FIELD1 FIELD2

DATA: T_EXTENSIONIN LIKE BAPIPAREX OCCURS 0 WITH HEADER LINE.

T_EXTENSIONIN-STRUCTURE = 'BAPI_TE_REQUISITION_ITEM'.

concatenate FIELD1 FIELD2 into T_EXTENSIONIN-VALUEPART1.

APPEND T_EXTENSIONIN.

Thanks so much.