You start off in the same room as everyone else. You'll have a name tag that has either Group A,B,C or D. I was group B and we toured for a bit first, then had our interview. Everyone in your group goes to a different professor/faculty member's office.
My interview was very easy-going. My interviewer wanted to talk about random things throughout my file and she asked me two standard interview questions: If you could go anywhere to learn a skill, where would you go and why? Also, she asked what page ___ out of 400 would say in my autobiography.
Good luck! It's pretty laid back!