ABAP consultant Working first time on APO Module

Hi all,

I have worked as a consultant(ABAP) for 5 yrs now on SRM and ECC and now will be working as anABAP consultant on the APO module.Please let me know some useful/helpful links as a starting point to know more abt APO module.Also what is different in APO when working on ABAP(Technical)?What are the objectsI should be concetrating more on?

Thanks.