There are two types of interview: Panel and MMI. Panel is the one where you have one/two interviewers asking you questions like why do you want to study medicine, what are your strengths blah blah blah (straightforward shit) MMI is one where there are 8-9 stations (so 8-9 interviewers) and in each station you are given a scenario and you need to talk about it (some universities will give you a set of questions to answer, such as Monash). For more information, you can do a search on ATARNOTES because I am sure there are posts after posts about medical school interviews

To be honest, don't stress about the interview because there is a chance you don't do well in your UMAT (not trying to discourage you, I am just stating the fact that UMAT is a hard/weird test and many people cannot get the score that they need)