IIT

Hello Arif,
It's good to hear that you have such a high ambition in your career. As you have set your ambition so high, so you should also be aware that you need to work really hard. You should understand the basics of physics, chemistry, mathematics and computers that you will be learning in class 11th and 12th.
You should ensure that your marks are above 80 percent in class 12th board examinations. Along with these, you also need to prepare for competitive exams. Books for preparations for IIT-JEE / AIEEE are easily available in the market. It is recommended that you join a good IIT coaching institute as well. They will help you to understand the concept better. They also take periodic tests which help you analyze how much are you prepared and how much more effort you need to put.
Then, you need to apply and appear for IIT-JEE Mains and IIT-JEE Advanced after completing your class 12th board examination and score good.
I wouldn't recommend dropping a year or so after class 12th board examinations for preparations for competitive entrance examinations.
However, I would also advice you to appear for other entrance examinations as well. This serves as a backup plan if things don't end up as per you had planned. You should also appear for AIEEE and state level examinations (COMEDK for Karnataka, EAMCET for Andhra Pradesh / Telangana, OJEE for Odisha etc.). The more the entrance examinations you appear for, the more options you will have for choosing colleges.
I hope it helps. If so, kindly upvote this answer. In case you have any further questions, feel free to revert.