Individuals carrying on an enterprise are entitled to an Australian business number (ABN). It is the simplest and cheapest business structure.
If you're a sole trader, you are:
You can employ other workers, but you cannot employ yourself.
As a sole trader, you are responsible for your own super and the super of any other workers you employ.
If you have been engaged to carry out activities as an employee, you are not entitled to an ABN for that activity.