Settlement of costs on a maintenance work order to a COBU WBS element

Hi ,

I need to perform the following -

The COBU WBS element will be stored in the maintenance work order in a custom field. The custom program will be triggered from exit IW010027. The program needs to fetch the WBS element from the custom field and populate that as the settlement receiver in the maintenance work order.

The settlement rule should be generated automatically at the time of closing the work order.

Can anyone explain in brief what is to be done after finding the above mentioned exit (I'm new to this technology)