Hi, so basically if you are interested in BITSAT and JEE exams you have to have PCM in your 12th.

Now to the application procedure is very simple. You just have to fill out your application in their portal online and there you go.

You will recieve your admit card in their website only. And the exam will probably be in the next week.

Just go to their online portal and fill out the necessary details and you are good to go.

And JEE advance is only available for students who clear their JEE mains exam, so you have to first clear your JEE mains exam.

And coming on to your next question, so basically UG and PG is just a term for graduation. Like UG is under-graduate like anybody who have their bachelor's degree/ diploma like BTech, BCA, BSC etc is an undergraduate (UG). Similarly, anybody with a master's degree like Mtech, MCA, MSC is a postgraduate (PG).

Hope this is helpful.