BAPI problem

hi friends,

iam new BAPI. this is my problem summary. pls help me.

1. I want to create Custom BAPI to display list of internal orders based on company code.

2. the external system sends business unit as input to the SAP system. this business unit is mapped to ZMAPPEd table.

3. The company code in COAS is mapped to business unit in ZMAPPEd table. based on that i want to download all internal orders and description in flat file.

4. For mapping they mentioned use BDc or call transaction.

flat file contains.

BUKRS fuknr Ktext

pls help me.

chandu