If you've received a discount code, you will be prompted to enter it in AFTER you go through check out and BEFORE you finalize the amount paid.
The discount will be applied to the original purchase amount, which does not include taxes and shipping. Tax is calculated on the price AFTER the code is applied. Shipping is also added to the amount, and must be paid.
GIFT CERTIFICATE discount codes for a dollar amount:
As with a % discount code, a $ discount code will be applied to the original purchase amount, excluding taxes and shipping.
If your gift certificate discount code amount is LOWER than your purchase amount, you will be required to pay the balance (as well as the tax only on that balance). All new discount codes generated for your balance will be sent to you via the email address associated with your purchase. Also, because this $ amount essentially brings your purchase to $0, this eliminates the need for taxes to be charged (as tax on an amount of $0 is in fact $0).
If you have any questions, or need assistance with using your discount code, please contact firstname.lastname@example.org