Store credit is an amount that is refunded to a customer account. You can use their store credit to pay for purchases, 


To apply store credit to your current purchase. First, please log in to your customer account with the same email the store credit was applied before beginning the checkout process.


When you are in your shopping bag under your order Summary your store credit total will appear under your Order Total.  See the example below.  



The amount of store credit that is applied to the order appears with the order totals and is subtracted from the grand total.  The available balance is adjusted when the order is placed.