idocs

hi i'm new to idocs here i had created custom idoc,inorder to populate the idoc i know we have to write a program of structures of edidc and edidd,i know all that but where we have to write the code,and what is the use of partner profile,what we will do there,plz guide me in this,i'm new to cross applications and bapis,plz help me out by guiding me in a right way,i had read many books on ale,idocs and bapis.thanks in adavance.