Hi Mani,
First the FM provided only for example. You need to find suitable one in your case based on WE20 setup. refer to standard ORDERS message type configuration if any in your system.
Based on configurations in WE20, EDIDC will be automatically filled. But if you need to change then there will be other exit also available.
EDIDD is for the data segments (header+item) which will have a segment name and specific data structure.