Hi 

You need to score minimum 75% marks in your class XII board exams or need to be in top 20 percentile in your respective board to be eligible for admission through JEE Main and JEE Advanced. Candidates belonging to SC or ST categories need 65% in their class XII board exams.

Check the complete eligibility here:

https://engineering.careers360.com/articles/jee-main-eligibility-criteria

https://engineering.careers360.com/articles/jee-advanced-eligibility-criteria

In order to be eligible for IITs/NITs/IIITs and GFTIs you should have 75% marks in your board exam or you should be in top 20 percentile.

For SC/ST you should have 65% marks. 

To take admissionin DTU and NSIT you should have 60% aggregate marks in P/C/M. There is relaxtion of marks for reserved category.

There are many private colleges as well who consider JEE Main score to provide admission. Eligibility criteria varies college to college. You have to apply for the application form seperately.

To check the list of the exams you can refer below link

Top Private colleges through JEE Main

Good Luck!!