application for visa to china

Hi, so it's my first time applying it. I was born in Australia and I want to travel to China during this holiday with my dad. I'm 19 years old and I just applied for a new adult passport yesterday. We are planning to go hong Kong as well after a few days staying in China. Was wondering how I could apply for a entry permit. Do I just go up to the office in St kilda then ask for a form to fill in and submit it or is there a link where everything could be done online.

To be exact, my dad will accompany me to Hong Kong then he'll travel back to China and when we're about to leave he'll travel back to Hong Kong to pick me up in order to take the flight back to Australia from China. So what type do we need (as in what type of entry; single? Double?). And exactly how long will the application take to approve because we are departing on the 13th of January. Also what documents do we need for the application? We're going to use visiting relatives as the reason to travel. I heard we must present a copy of the relative's ID as well as a invitation letter.

Sorry for all these question since it's my first time applying and haven't traveled for nearly 6 years. It'll be a great help if you could have the time to respond back.

Thank you so much!! :)