Admissions into IITs is done on the basis of JEE-Advanced rank and that of NITs is done on the basis of JEE-Mains rank. The most important requirement for getting into IIT is to qualify JEE-Advanced and 75% aggregate marks in class X!! boards or or be in the top 20 percentile of your respective boards.

You are expected to have ample knowledge in PCM. So in order to qualify Advanced you'll have to learn the basics mentioned in the boards syllabus.