Hello Abhinandan!

You will get to know your branch then and there itself at the time of counseling. The entire counseling and the allotment of branches to students is computerized. 

When you receive at your given place, they will call you according to the rank that you have secured. They will give you certain necessary applications and documents to fill up, mean while they will verifying other important documents of  yours such as your birth certificate, board marksheet, etc. So in those documents given to you, you need to mention your desired branch in your selectivity order. You will have around 4-5 choices. For eg-:if your first priority will be CSE,second will be IT ,third will be CSSE ,fourth will be CSIT then you need to mention that in order. 

If your rank is within 3k you can get CSE or IT branch (taking last year cut offs into consideration) . There will be a number of screens infront you at that counseling place where you can see the number of seats remaining for the given branches as well as which candidate has chosen which seat. In this way you can have an idea which seat will be alloted to you as per your preferences. Mostly CSE and it's derivative branches fill up faster due to the increasing demand. 

Hope this helps! 

Stay in touch for further queries! 

All the Best!!!!