confirmation control key

hello gurus

what is confirmation control key. how it is used in creating po. and then gr and invoice receipt. what is inbound delivery,rough gr ,order acknowledge inside the control key. please explain me with one business process .if any one have snap shots please send it on my mail id- chhikara_krishan@rediffmail.com.

handsome points will be rewarded.thanks

regards

k.chhikara