You will be shortlisted based on your board score. The selection process is followed by a computer-based aptitude test and a personal interview session. My friend appeared for this exam and she had mentioned that the mathematics section was taken from JEE Main and there were certain questions based on logic.
The interviewers would ask for certain proofs of whatever you have accomplished. So, you would have to carry along your certificates as they ask about your participation in extracurriculars and look at the certificates as proof. These certificates can be of anything you have partaken in dancing, singing, drama or any other activity you like.
In the interview, they will consider things like your JEE marks, passions, and ambition in life. Plus, the obvious- why do you want to take admission in SSN College, and what all options do you consider as your backup options. This entire interview process checks what kind of a person you are in terms of talent. It will be an advantage if you can speak fluently in English.