The subjects in first sem. Of Btech. In any of the field are same.Generally you have to study Engineering Mathematics,Physics, Chemistry,Machine drawing,C programming etc.These are just a elaboration of your 12 th standard syllabus.As you opted CS then you should start programming as per your interest and also it is required for placements.I would recommend you to learn coding in C,C++ in your first sem. rest you will figure out in your graduation.
All the best for your future and chill out in vacation.

Hey,
Physics
Mathematics 1
English
Basic Electrical
Are some of the subject
Note that all the subject are common for the first year students irrespective of their branches.
Hope this works