The Bachelor of Nursing can be studied at university. If you become a Registered Nurse you need to be registered with the Nursing and Midwifery Board of Australia, so you need to make sure the course you complete is approved by the Board. Visit https://www.ahpra.gov.au/education/approved-programs-of-study.aspx?ref=nurse&type=general&div=registered%20nurse%20%28division%201%29 to check the course you are looking at is approved before you start study.
You may be eligible for a Commonwealth Supported Place, which means the Australian government pays for part of your course costs. Visit https://www.studyassist.gov.au/help-loans/commonwealth-supported-places-csps for more information on Commonwealth Supported Places.
Talk to your teachers, guidance officer and career advisor for more information on whether this course might be suitable for you after you finish Year 12.