A copy and paste from the gift certificate ad page(s).
"...Penguin Magic Gift Certificates are delivered in the form of "Gift Codes". We will provide you with a Gift Certificate Code via email (normally within 24 hours). You can give the gift code to your recipient any way you like (in a gift card, by email, etc.). When your recipient is ready to place an order, he/she can pay by simply entering the gift code in the "Gift Certificate Box" during checkout."
That's it!