Hello,

You need to qualify the JEE Advanced exam in order to get admission to B.Tech course in IITs. And firstly, you have to qualify the  JEE main exam. Eligibility criteria for JEE main exam is you should have secured at least 75% marks in the 12th class examination, or be in the top 20 percentile in the 12th class examination conducted by the respective Boards. For SC/ST candidates the qualifying marks would be 65% in the 12thclass examination.
Good Luck!