First of all you need to write an entrance examination like Jee mains, jee advance, cet, comedk, bits, etc. And also you need good percentage in your Pcm and also English subject in your boards as per the eligibility criteria of these exams. And then as per your merit score in the entrance exam, you've to go for the counselling and then fill up the colleges choice list as per your convenience. And then according to your merit rank, you'll be granted a seat in a particular college considering your choices.

Refer to the site below for more detailed information..

https://engineering.careers360.com/articles/all-you-must-know-about-engg-admissions

Best wishes. Thank you .