If you are ForEx/CFD trading for profit making as a side gig (not like carrying on a business) add up all your profits and declare this total profit (not net profit) from Forex/CFD trading at "Other Income" sections (more info at https://www.ato.gov.au/Individuals/myTax/2021/In-detail/Other-income/?=redirected_mytax21OtherIncome ). Even though you made an overall yearly net loss, you should be decalring your intermittent total profits per asset (total profit for going short/long positions per asset) in this section because these total profits need to be added to your assesseble income to be factored into your "Income Test" to calculate your different liabilities like medicare levy surchagre, HECS debt repayment and so on... You can request a yearly itemaised realised P&L statement from your CFD trading platform provider unless they have sent you one already at the EOFY, which they should for tax purposes if they are a CFD trading provider in Australia).
AND add up all your CFD positions close losses per asset for the year (not net loss) from Forex/CFD trading and claim it in level D15 (more info at https://www.ato.gov.au/Individuals/Tax-return/2019/Supplementary-tax-return/Deduction-questions-D11-...) So ultimately you are paying tax on your net taxable profit/income.
If ForEx/CFD trading is your business then fill in business income and expenses sections in details. Only exception is you wouldnt be able to offset the Forex/CFD losses against your other incomes. Losses must be carried forward until you are eligible to offset it against similar income in later years just like other business income and losses treatments (more info at https://www.ato.gov.au/Business/Non-commercial-losses/)
CGT doesnt apply to Forex/CFD trading profit/losses because you never owned the underliying asset to begin with.
And there is no GSTs in Forex/CFD trading.
Hope this helps and correct me if I am wrong or missed anything here!