Hi, Dani,
First, have a look at the Family Law Courts website on divorce, which is
here. This gives you plenty of information about filing for divorce when you were married overseas and when your spouse still lives overseas.
For brevity's sake, all you need to do is file a divorce application (found
here) to the Family Court of Australia. You will need an application kit and a copy of your marriage certificate to do this, and your application will need to be witnessed either by a JP, or a clerk of the court.
The filing fee is currently $800, but if you are entitled to a concession discount (if you are on benefits of some description, such as family support, etc.), it will be more like $265.
You will need to serve your former spouse with a sealed copy of your divorce application (that is, a copy bearing the seal of the court, which will be stamped on the day you lodge) at least 42 days before the hearing date. If you do not know where your former spouse lives, there are provisions for this complication outlined in the application form.
A divorce application is not at all complicated to do yourself, and in fact, I would strongly advise doing it yourself, since there is no property settlement or kids involved, which means it would be swift and simple. Drop by the Court Registry if you live near one and have a chat to one of the clerks. They will be able to give you more guidance on what documentation you need, but in the meantime, have a look around the Family Court website for more information.
Hope this helps.