which code is used for read the data from ci(communication 
idoc) and it stores the data in perticular data base table.
that code is process code.

ex  : matm .
it reads CI and stores the  data in mara table.

process code is the function module in which the code to 
capture the idocs that was sent by the sender(outbound)and 
to update in the database table.

Example : matm

Processing Code determines point to which an idoc has to be 
sent for furthur processing.

This can be a program or triggering a BADI or a function 
module.