Undergraduate - after completing your high school education, you can directly apply to australian universities . The programme is of five or six years duration. 

Postgraduate- if you have already received a bachelors degree in medicine, then you are eligible for graduate program. The program are of four years duration. 

The Australian National University Medical School (ANUMS) is one of the top school to pursue medicine in Australia. Since you have not mentioned whether you want to pursue medicine directly after you high school or after your graduation. I am giving you details of both the scenarios. 

1) undergraduate -