Trigger Ariba NetWork x Ariba Seller (Vendor) integration

Hi Ariba Experts

Please I started to do a P2O integration so I got a doubt :

Company creates a PO in ECC, The PO created is sent to Ariba Network ,  and forward to Supplier through Ariba .

So when the supplier log in into his Ariba Supplier portal, it will be able to see the new PO Received.

My question is :

How Ariba Network was able to send the PO to Ariba Supplier ? where is done this customisation ?

Is there any need of manual intervention inside of  Ariba Network or will be send automatically to the Supplier?

Regards

Marcel H.