Hello Aspirant! After giving your JEE Main Examination and getting your percentile marks and rank you can participate in the JEE Counselling on the official website of JOSAAA which is conducted after JEE Advanced. You can chose and arrange the colleges according to your priority and if you qualify the cutoff marks of that college you will get admission in that college and branch itself. Then you need to pay the fees to book your seat and your admission will be confirmed.
You can also use this link to predict your college:
https://engineering.careers360.com/jee-main-college-predictor?utm_source=qna&utm_medium=jee_cp