Hi Jimmy,
Another good place to read through -
http://www.ato.gov.au/businesses/ent...x?menuid=43539
This section of the ATO will help understand your business situation and the sorts of records you must be keeping etc.
If you intend to operate a business - you must have an ABN. If you will be operating it as a sole trader, then it is
your ABN; as TehCamel mentioned you can then register a trading (business) name, which you
must do if trading by any name other than your own. When you register a business name it will ask you as the sole trader if you have an ABN already and ultimately it will be linked up.
You have asked if when you receive payment via PayPal do you call it income tax or business activity. It would be business income - income tax is what you pay for earning the income - the initial payment through PayPal is not income tax itself. Again as TehCamel already mentioned - how and what is paid in tax will depend on the structure of your business. If you operate as a sole trader then even if you have a different name registered for the business name the 'entity' is you personally, so the money the business makes/spends will likely have a direct impact on your personal income and therefore your income tax. If, for example, you registered a company (e.g. Pty Ltd) then it is its own entity and would need its own ABN and would pay its own tax on profits etc; payments to you from the company would essentially be "wages" and you would then do your own taxes etc at the end of each year 'as normal'.
You will also need to register for GST once turning over more than $75,000 so you need to keep an eye on what the business bringing in.
If operating as a sole trader then also consider a separate bank account for the 'business income' etc - this will help track incomings/outgoings to properly work out tax and things come the end of the financial year - it can be a bit messy to just have it going into your personal bank account.
All the best with it!