A tax return is when your employer has withheld tax from your pay, but sent too much to the ATO on your behalf so the tax office refunds that to you when you advise them of the total amount you earnt for the financial year.

I think you do need to put the info on the group certificate into your tax return, Mabello, because this pay affects your total income for the year, even though you may not have paid tax from it.