I want to migrate data from sage to Netsuite, does any one having documentation or any idea about it

if you go to help center or Suite Answer there is a User Guide for CSV import

This is a very open ended question that has many answers depending on what you want to do (opening balances/full transaction history/open transactions only/blahblah) etc. I strongly suggest talking (ie: paying) to somebody that knows what's involved

beginner