What is the appropriate way of displaying messages during BDC

Hello dear experts,

I have a requirement that for the transaction ME22N (PO) I need to mass upload the confirmation category as 'LA' for each item if CC(EBTYP) isn't present in the first place by BDC call transaction. If at all CC is present, as 'AB', it should display a message as "Confirmation is 'AB' for this item" and then it proceed with the next item (EBELP) of the particular purchasing document (EBELN).

Here I'm in search of two things.

1. How does it give a message during upload? What is the appropriate way of coding for this type of message? 

2. If one item is done, how does the next item come into picture ?

I'd be grateful if you could help me with this.

Thanks and regards,

Ambareesh J.