need help in user exit !!!!!

have two requirements like

1.When the SAP Sales Order is shipped a SAP iDoc “DESADV” will be triggered. – Note This idoc already exists.

2.When a Credit Memo (Billing type G2) document is ctreated – an iDoc should be triggered.

I want to get the name of the user exits for both the cases. Where I can associate the idoc generation code.

I have less time.

need help.