Hi Kiran,
If I understand correctly, your integration is for Purchase Order Automation / Invoice Automation.
Which doesn't require any of the Ariba Component other than ASN.
You could find ample document in connect.ariba,com for step by step guide.
I'll suggest you to use AN_Adapter_NetWeaver_12s2.pdf & AribaNetworkIntegrationGuide.pdf (Easily available in connect.ariba.com).
Thanks
Subhash