If you decide that a company structure best suits your business, then you need to register as a company. By registering a company name you have the advantage of having exclusive rights to that name in Australia, without having to register in each state.
You can only choose a company name not already registered to a company or business. Special approval is also required to use certain words.
If your company carries on business in a name different to your company name, then you must register the business name in the appropriate state or territory.