Hi Shahid,
here are my answers:
1) business packages -> SAP enterprise Portal Administrator
function module -> ABAP Developer
2)Business package -> package for enterprise portal which contains portal content like iviews, roles etc. BP have to be implemented in enterprise portal
function module -> something like bap program in the backend, can be called in other programs and has a defined interface
3)You need the BP's to display eRe content in the portal. Function modules are part of the eRe backed functionality. Those are already installed in then backend.
4)No
5)There is no list of function modules. The BP for eRe can be downloaded from service market place
hope that helps..
BR
Martin