Mannu,
Configuration would depend upon the current solution, and the detailed business requirements of the to-be solution.
In addition, APO has several planning engines, each of which would require different answers.
I suggest you consult with local experts to figure out exactly how the currently implemented solution works before you venture into creating additional functionalities (like planning at the warehouse level). Or, if you wish to self-train, try reading the basics, found in sap online help:
Supply Network Planning - SAP Library
Production Planning and Detailed Scheduling (PP/DS) - SAP Library
Capable-to-Match (CTM) - Multilevel Supply and Demand Matching (SDM) - SAP Library
In addition, within Supply Network Planning, there are two major planning methods; Heuristic and Optimizer:
Comparison of the Planning Methods - Supply Network Planning Run - SAP Library
If you are unfamiliar with APO, and you have never done such an implementation, you would probably want to use experienced local solution architects for this project. If such SAs don't exist, the common method used is to hire a consulting company with expertise in these subject areas.
Best Regards,
DB49