Badi for PO confirmation **Urgent**

Hi,

I want use a badi when using transaction COR6n.

The implementaiton name is /SAPTRX/PP_WOCONFIRM.

Interface name IF_EX_WORKORDER_CONFIRM

1. Can anybody please tell me what is the difference between the methods at_save and at_cancel_check??

2. how should I proceed with this if i have to use any of this method when confiming process order in cor6n?