JEE Main Exam is conducted for admission to prestigious institutes like NITs, IIITs, CFIs of India.
While JEE Advanced is another exam ahead of JEE Main for admission to IITs, ISM Dhanbad and IT-BHU.

For appearing in JEE Advanced, you will have to qualify JEE Main Exam.
And, the Merit list of JEE Main would be prepared by including 40% marks of your XII Board Exam and 60% marks of your JEE Main Entrance Exam.
So, you need to work hard on your Board Exams too.

For qualifying JEE Main Exam, you must score above 130 marks to qualify it.
But if you wish to get a decent Government College for better shaping of your future, then you must score 240+ with Board Marks above 85%. Since, the competition is getting tough now year by year. So, you may face much more competition in the coming years.