To apply for an Australian visa, you have to know the purpose of your stay. Is it a holiday, visiting family or friends, transit, working holiday, business visitor activities, medical treatment, volunteer work, etc.?
For every purpose there is a different link to click on when you go to the website. The official way to apply for a visa is via the website of the Australian Government. You can apply for a visa through third parties and pay some extra costs, but there’s no need for that, because here is a step by step explanation about how you can apply for a visa yourself!