server not found

Hello i am working on BW 7.0 and iam very much new to BW.when iam using business explorer to see sales forcast or any other report iam getting error in browser as firefox cant find the server at bwserver6.domain.com and administrator is suggesting me to Add the line below to your host file:

64.72.230.45 bwserver6.domain.com which i really dint understand ?how to add entry to host file?please help me i this regard.your help will be greatly appreciated.

Regards

janapathi