tax file number is a personnal ID, you can say it like that. when you work or deposit your money in any banks in australia, you need the TFN. otherwise you will be charge the most high rate for your income or your bank interest. if you haven't any deposit or no job in australia for the time being, you also can apply the TFN firstly and keep it for your future usage. you can tell the aust. taxation office mail the number to your friend's home if it's security or you can do it next time when you land for a long time. I strongly suggest you to do it NEXT TIME.