Probably nothing!
Majority of students, esp. the ones who have been busy having coaching for JEE Mains join the college as no knowledge about CSE. If you have super zeal, enthusiasm and motivation about Computer Science, you will learn them with time. In first year, you probably have one or two courses of computer science. I had only one ,namely C-programming. It is not that difficult to learn it. If you’re completely blank to it, try to grasp the idea of C programming. Slow by slow but with continuity, you will know it good.
Have a chill-pill , don’t worry. Hold your excitement, you have made a fantastic decision by opting Computer Science. It is really fruitful, in demand these days and you can easily perform practicals as compared to other branches.
Happy Engineering, cheers!! 🙂