TL;DR - my understanding of the rules is that if you are required to register for GST (earning more than $75k per annum), you would be required to pay GST on these items.
To clarify firstly: taxable income, and goods and services tax, are two different things.
Any income you receive needs to be considered for income tax purposes - whether or not it ends up being taxable income would be too much to go into here, but generally you would take your expenses, and any deductions, away from your income to arrive at what would generally be the taxable amount. An accountant will help you do this.
Income tax is paid by anyone who earns income over the tax free threshold.
By contrast, goods and services tax is a tax paid by business (of which you are running one). Of course, this is passed on to the consumer, but it's the business that remits the payment to the tax office. However, GST isn't required to be charged and paid in all cases:
The key in your situation is first determining whether you need to register for GST (or whether indeed you already have). If you earn less than $75,000 per year - no need to register.
If you do earn more than that through your business, or you have registered anyway, then the next question is whether your items are GST-free. The ATO says that "some education courses [and] course materials" are GST-free. Whether this applies to you or not I'm obviously not going to be able to comment on, so I would advise getting an accountant's advice on this (or at the very least, call the ATO or browse their legal database).
Thirdly, are your sales connected with Australia? The ATO says that "A sale of something other than goods or property is connected with Australia if ... the thing is done in Australia [or] the seller makes the sale through a business they carry on in Australia". Both of these appear to be true in your case.
So in summary: if you are required to register for GST, you would be required to pay GST on these items.
I am not a financial advisor or a tax accountant and this is not financial advice.