Most professional schools require a personal interview. The interview helps them evaluate your preparation for their program as well as your social skills and your fit with that school.
Interviewers are typically faculty members, administrators, and students who may or may not be members of the admissions committee. Some schools have open files which means that the interviewer may have read your submitted materials. Others have closed files so the interviewer will not have read about you before your interview. Either way, you should be prepared to discuss materials from your application including work you have done, your extracurricular activities, interests, and hobbies. You should also be prepared to discuss current news events, issues in health care, and new scientific developments.