You're almost guaranteed to have this in your grad school interview questions. So prepare a list of five or more questions. The best questions demonstrate that you've research your field and the school's faculty members in depth. For example, you can ask the interviewer to talk more about his or her research: "I read your article on _______, which is a topic that corresponds with my own interests, can you tell me more about it?" You can also discuss specific aspects of the school's department, facilities, courses, or other peculiarities that show that you're a serious applicant. So have your own list of grad school interview questions in your back pocket.
Anything that can give reviewers a sense of you as a person belongs here; you can repeat information about your experiences in your research statement, but any experiences that show your promise, initiative, and ability to persevere despite obstacles belongs here. This is also a good place to display your communication skills and discuss your ability to maximize effective collaboration with a diverse cross-section of the academic community. If you have faced any obstacles or barriers in your education, sharing those experiences serves both for the selection process, and for your nomination for fellowships. If one part of your academic record is not ideal, due to challenges you faced in that particular area, this is where you can explain that, and direct reviewers’ attention to the evidence of your promise for higher education.