The interviewer may have read your application and be quite knowledgeable about you and your candidacy, or the interviewer may not know anything more about you than your undergraduate institution. In the latter case, you should be prepared to fill in the interviewer on the important aspects of who you are, what you have accomplished, and what you see as your strengths. In the interview in which your interviewer has read your application, you might expect more specific questions. You may have one long interview, two shorter ones, or one short one. You may be interviewed by admissions staff or admissions committee members, who are faculty at that medical school.
Some schools use students as interviewers also.
You can expect to be nervous in this situation, but we can assure you that for the most part, interviews are not designed to give you a hard time. This is not to say that you won't find the situation a little stressful, but in general the schools want you to feel comfortable so that they can learn more about you. Beyond these, there are many other possible questions. Remember, the schools are trying to get at subjective qualities, like leadership, compassion, motivation, integrity, maturity, curiosity, judgement. We have appended a list of questions which our students have been asked in the past.