If you have been credited some store credit by our Customer Service, or you have redeemed a e-Gift voucher on your account, you can find the available store credit in the last page of the checkout (Payment step).
The store credit is visible on the top right corner of the page, and to use it you simply need to click on it. If the store credit is enough to cover the full value of your order, then you can simply click on Place Order. If not, you will have to pay the difference with another payment method (i.e. credit card).