Regarding custom idoc

I have created 4 segments z1 with fields eord-lifnr,lfa1-name1

z2 with eord-matnr,maky-maktx,bdmng

z3 with mard-werks,eord-ebeln,eord-ebelp,eord-meins,mard-labst+mard-isme,period,begin_date,end_date

z4 with bdmng,datum

then how to declare the edidd,edidc,edids,etc

HOW TO POPULATE THOSE FIELDS?