Hello dear,

See for getting admission in iit you have to clear two entrance exams . One is jee mains and other is jee advance . Firstly you have to clear  jee mains with a good score and than you have to get under 10k rank in jee advance to get a good idea . In addition you should have a minimum of 75% in pcm in class 12th . So start preparing and clearing of concepts is most necessary thing in clearing any of the exam.

All the best for your future.