There are three main assessments used by medical and dental schools to select students: the ATAR, the UCAT, and the interview. Each of these assessments is designed with a different purpose.
The ATAR is designed to assess the breadth of your knowledge and your ability to learn in a formal educational setting.
The UCAT is designed to assess your ability to make evidence-based decisions across a variety of contexts, as well as your ability to apply basic ethical principles to medical scenarios.
Finally, the interview is designed to assess whether you possess suitable traits to work as an effective medical student and doctor, and especially whether you possess the skills that are needed to develop trust-based relationships. There are a wide variety of traits they’re looking for, including qualities such as being honest, empathetic, or good at problem-solving, but they’re specifically looking for the medicine/dentistry-specific versions of those traits (and not just whether you’re an empathetic person in general, for example).
Since many of these traits can’t be identified through written assessments, the interviewers will try to identify the traits in person: they’ll listen to what you have to say, and then use that to assess whether you truly are what you say, and how you would behave in different situations and respond to different matters. If they can see that you possess the traits they’re looking for in their medical/dental students to a well-developed extent, you’ll be rated well, but if you don’t demonstrate some (or all) of the required traits, this will be reflected in your score.