When you want to travel and stay in a different country you need a visa to do so. For Australia, the most common visas used to enter the country and then live there for a time at least are the business visas and the student visas. Each visa that you can enter on though has a different purpose and the amount of time and what you are allowed to do in the country varies depending on the visa you have.
For example, on a student visa, you can only stay in Australia until you graduate from university. If you are on a business visa you can leave and re-enter as often as needed for that project, but once it is complete you cannot stay past it. The business you are working for would have to say how long the project will be, there are no open-ended business visas. It is always a very good idea to use a leading migration agent, in Perth for example, to ensure you come in on the right one.
If you want to come in on an Australian work visa there are two basic options, temporary visas or permanent. This allows Australian businesses to hire people from outside the country when they need a specialist or they just cannot find Australian workers for the job. On a temporary visa, you could be working in Australia for anything from a year up to 4 years. You can apply for permanent work visas when you are in the country on a temporary one. Again something your leading migration agent in Perth can help with. Your employer can also extend the work visa for another 4 years if they want you to stay and you agree to it.
If you do apply for permanent residency and you meet the requirements you would then be able to live in Australia for as long as you wished and you would be able to go back to the country you are from, then return to Australia as you wished.
When applying for a student visa the subject you want to study is a strong part of their decision as to whether to let you in. Some subjects are not as valued as others in Australia and if they decide your subject is not worth it, then they will probably say no. Subjects not viewed well include general studies, leisure studies, and philosophy as they do not lead to a specific and useful (to the Australian government) career as they are just too broad.
When you apply for an Australian student visa with the help of a leading migration agent, in Perth, you will need to state your field of study. If you are successful in your application of a student visa when you graduate you can apply for a permanent residency visa if you do not want to return back to your home country.