Student Visas are for people who have a guaranteed place on an approved course at an Australian school, university, or other recognised educational establishment. It is a temporary visa, and is granted to cover the time it will take to complete the course. With a Student Visa you can also work in Australia, providing you are old enough.
To apply you must be enrolled on your course. Your English skills have to be suitable, and you need the financial means to support your stay in Australia. You also need health insurance covering your entire stay. Additional requirements are placed on students who are under 18. They must have parental permission and it has to be shown they will be properly looked after, i.e. have somewhere to live and someone responsible for their welfare.