You can see how many gemstones you have accumulated by logging into your account, then clicking on the 'MY ACCOUNT' link from the main menu.

To redeem gemstones for order discounts, click on the Rewards link from the top or bottom menus to open up the Gemstones user interface panel.

Once the panel is open, you can see the available options to redeem your gemstones for voucher codes. The voucher codes can then be input at checkout.