>>1)what is the option of export/import utility for to generate archives while we we are performing export or impot?
You did not mention your Oracle version, If your DB version is >10g i'd suggest to use Datapump method for Export/import, it is faster then normal one
at the time of Exporting data Archival is normal while at the time of import it grow Fast.
Check this Article for start :ORACLE-BASE - Oracle Data Pump (expdp and impdp) in Oracle Database 10g
>>2)if i have already existing table in my target database, my requirement is again i need to some more data from source Database to target Database using export/import, how can i perform this? using just ignore=y while import or something else
yes, in Normal Imp command you can use ignore=Y, however if you go for data pump you can use parameter TABLE_EXISTS_ACTION=APPEND