To get admission in BITS Pilani (any of the three campuses of Pilani, Goa and Hyderabad), you have to give and exam called BITSAT (Birla Institute of Technology and Science Admission Test).

After giving the exam, immediately you'll be shown how much marks you have scored, and then depending on the score cut-offs, you'll get admission into one of the three campuses in the counselling.

All the best!