Dear Aspirant,

To do Btech from IIT, you have to give the JEE Advanced Exam and to give JEE advanced exam you need to give JEE Main exam.

Essentially, JEE is Joint Entrance Examination for admission in various engineering colleges, and it is conducted in two phases. The first, Main is for admissions in NITs, and to be eligible for JEE Advanced, one has to clear the JEE main and should have a minimum of 75% in their +2 (top 20 percentile of respective board)

In JEE Advanced, after the results a rank list is published and after that a counselling process is done, which basically asks you for your preference of the IITs, and allot you a seat in the IIT for which you have enough rank.

Hope this helps. Thank you.