Your cashback goes into your store wallet, and is spent like any other balance in it.
The steps
1. Sign in to your account — the balance is tied to your account and will not show without it
2. Add your products to the cart and go to checkout
3. Your available balance appears and is applied to the total
If your order costs more than your balance, you pay the difference by any payment method. If it costs less, the remainder stays in your wallet within its validity window.
Worth knowing
The 299 free shipping threshold is based on your cart value, so using your balance does not affect your eligibility for free shipping.
You can track your balance and its expiry date from the wallet page in your account.