Question: how much study we have to do be a docter

There are different pathways leading to the title “doctor”. Before explaining the pathway, let me clarify a disambiguation. The doctorate originally appeared in medieval Europe as a license to teach at universities. Its roots can be traced to the early church when the term “doctor” referred to the Apostles, church fathers and other Christian authorities who taught and interpreted the Bible. “Doctor” means “to teach” in Latin. Nowadays people call physicians and surgeons as “doctors” and this is not wrong. However throughout much of the academic world, the term “doctor” refers to an individual who has earned a degree of Doctor of Philosophy, or Ph.D.
Coming back to your question I’m not sure which “doctor” title you asked for but I’ll explain both of them.
If you wonder about physicians or surgeons who are also referred as “medical doctors”, there are two pathways:
1) After Year 12, you can sit on “undergraduate medical & health sciences admission test (UMAT)” followed by an interview. If you are successful you can enter into 5-6 year-long medical school where you will be studying Bachelor of Medicine & Bachelor of Surgery.
2) After Year 12, you can study any Bachelor’s Degree. Upon completion of Bachelors Degree you need to sit on “Graduate Australian Medical School Admissions Test (GAMSAT)” followed by an interview. If successful, you will gain entry into 4-year-long graduate medical school.

When you finish medical school, you graduate as Junior Doctor and you can enter the medical workforce.
When it comes to how much study required for it. Well, a lot.. However you don’t need to be smart or genius for sure. Anyone with a good memorisation skill can become a medical doctor because all the admission tests including medical tests don’t measure your aptitude instead they measure how good you can memorise knowledge – it is a very important skill for both surgeons and physicians.

If you wonder about doctors in academy – people who earned a Ph.D. – the story is a bit different. Basically after Year 12, you have to enter into a Bachelors Degree of your interest. It could be science (ie. physics, maths, biology and related areas) or engineering or history etc… Once you graduate, you have undertake a Master of Research Degree or do Honours Year. In the meantime, if you still feel passionate about whatever you are studying, you naturally start asking questions about certain topics of your interest. Once you decide what you want to work on for the next 3-4 years, then you have to find an academic supervisor who can support you in every way. Once you find a topic and a mentor then you can apply relevant academic departments of universities to get admission into Doctor of Philosophy. You undertake an intensive research during your PhD – usually addressing a question or a problem. You are required to write a thesis which will be reviewed by academic peers in order to successfully graduate. Once you finish your PhD then you earn the title “Doctor”.
In order to be successful in this pathway, you have to develop critical thinking skill – this is very important. If you are smart or intelligent that helps for sure but not necessarily defines the eligibility criteria. You have to be hardworking, curious and inquisitive, passionate plus you have to develop good and effective reading/writing skills, you have to be able to perform multiple tasks and the most importantly you need to be able to ask Why and How questions and develop critical thinking. Unlike medical doctors, you don’t need to memorise and pass tests in order to be successful instead you have to be passionate about whatever you are studying and you have to be able to ask questions and establish methods to find an answer. Do these and you will never regret, you will be the happiest person in the world. Science is awesome when you start feeling for it.
By the way, my apologies for the looong paragraph, I hope I didn’t make it boring while attempting to answer your question.