If you are a new resident of Australia and have never had a tax file number (TFN) then you need to apply for one. Many schools assist their students in applying for a TFN as part of the year 10 program, so most high school leavers should have one. If you don't have a TFN then you'll need to apply using one of the methods set out in this ATO link - click here for more information.
If you are entering the workforce for the first time there are age limits for working in Australia - read more here from Youth Law Australia.
If you are starting a new business or activity, we advise strongly against simply setting up a new entity or just applying for an Australian Business Number (ABN) under your name. There are several considerations and if you get it wrong there are short and long-term ramifications. Read our recent update on getting your business structure right. We offer a structure review service for those thinking of doing something new, email us at BDTeam@Primarius.net.au for the details.
There are a few requirements you need to meet for any new venture to be considered a business, as opposed to a hobby. These will need to be addressed before the ATO will allow you to apply for an ABN. If you aren't sure - contact us for more information.