No, there is not a tutorial in place for a gift certificate system.
You would need to have the user logged in before they could redeem the gift certificate, see the "Applying Register/Login to your checkout" for details on that.
then you would need to add custom logic to the checkout process to deduct the certificate from the cart, update the certificate if there is any leftover, the process the transaction through the gateway if the deducted cart amount is greater than 0. It shouldn't be to difficult to put this in place if you are familiar with PHP coding, but we will not be able to offer extensive support for this beyond a general overview.
