Oyye Mohit!
Hi
You should do Macroeconomics by Mankiw. It has excellent foundations for basic theory of macroeconomics. You can start with it considering you don't have economics background.
But, for ISI specially, you will need to dig a little deeper, so have a look at either Macroeconomics by Blanchard or Macroeconomic Theory and Policy by Willian H Branson in addition to Mankiw. They will give you a more sophisticated presentation of UG-level topics.