You can view your UrbanStems credit balance in your Account Dashboard. After you log in to UrbanStems, click on the link with your name in the upper right-hand corner next to the shopping cart. Select "My Account" from the drop-down, this will take you to your account dashboard. Available Credits will be shown in the top right portion of the page just above the Payment section.
You will also be able to view and choose whether or not to use your account credits towards your order in the payment section during checkout. There will be a checkbox next to any available credits below the payment section during checkout that reads "Use Credits". Check this box to apply the credits to that order.