If you intend to operate as a sole trader / individual select this option. You will be in business as soon as your ABN is issued.
If you intend to form a general partnership between 2 or more people select this option. Once you receive the ABN you can commence trading as a partnership.
If you have a Pty Ltd Company registered with ASIC and need an ABN select this option. Your company will be able to apply for a TFN, register for GST and PAYG.