Not as good as the recent Mother's Day sale (10% off and $100 voucher).
To apply for the $50 cashback, after placing your order, go to https://www.thegoodguys.com.au/offers and find your offer. Once the claim is approved, you'll be sent an email link to request a $50 visa debit or bank transfer.
To get the $80 voucher (to be issued on 14/07 and expiring within 7 days), simply select Click & Collect when ordering.
To increase the $80 voucher to a $120 voucher (same issuance and expiry), you'll need to pay via Paypal Pay in 4 (refer to this deal - https://www.ozbargain.com.au/node/703751).
Don't forget 2% cashback via Cashrewards or 1.5% cashback via Shopback, and use any discounted gift cards (e.g. Suncorp 5%).
Note the store credit for TGG isn't that useful, even with the 10% off that comes around every now and then.
Personally I'm waiting for a repeat of a 20% off deal (there was one from Myer in late april)