Interviewers help put a face to the stats, and in that way can be important for schools that use holistic review.
However, they likely won’t torpedo your application unless it brings up a red flag or you do something awful/say something very racist/sexist, etc.
To practice, do mock interviews with your parents, think of some typical interview questions and how you would answer them, but most of all, relax. Interviewing can be fun- it’s really just a conversation.