Hi Sandeep,
Hope you are doing well.
It is also good to understand the Master Data and Transactional Data used in APO as well as the SCM Basis features. This is are the basis of the APO application processes.
Understand the CIF (Core Interface Application) is a good one too, as this the interface that makes the communication between APO and ECC systems data.
Good luck!
Cheers,
Rodrigo