The student visa allows you to stay in Australia for the duration of your studies (and between one and three months more, depending on your course), and to return and leave the country as you see fit during this period of time.
If you want to earn some money, it's possible! You will need to find a small student job. However, do not exceed 40 hours of work allowed for two weeks outside school holidays where this limit is lifted. To know that students who study a Masters' degree by research or a doctoral degree (PhD), degrees focused on research, have no restrictions when working hours.
Also note that you can not work before classes start. If you plan to bring one of your loved ones, check with Australian immigration.