Hello,

You are under CU. Means Calcutta University student. Your subject is Science stream which is good. Now you want to apply prelim then it will be may any government examination UPSC or WBSC examination. But you didn't mention it above it's okay.

At first you need to download the syllabus of your examination. Then you have to prepare the basic mathematics and Aptitude. Which is most important. You have to focus on your English and english grammar. Then you have to study political science, sociology, history etc other subjects. And you have to aware of current affairs which are very important. You have to practice daily it will help you out in examination.

All the best.