Hello Nidhi,
At the orientation program, they'll introduce you to the dean and some of the teachers. Seniors will narrate their experience of the college and you will asked your personal details so that they can contact you for informing when the classes will happen. After the first day, classes are fixed. It is not compulsory to attend it, but it is advisable to attend it.
For orientation go through the link mentioned below
https://www.nmims.edu/students/new-students/orientation/