To create a gift card, You'll need to do the following:
In the main settings cogwheel, click on Giftcards in the lower section of the menu box.
Click on the Plus icon in the upper right corner to start creating a new gift card.
If the contact already exists, search for the contact in the box that pops up. If it's a brand new contact, click on the "+ New Guest" button, and fill in the relevant information available (New guest button outlined below).
If you'd like, you can click on the Details tab, and enter in a note for the gift card reason/context (Box #1 below). You can also manually adjust the gift card's expiration date here as well (Box #2).
If the contact information looks good, Click Save. Doing this will pull up the payment box, where you can specify the gift card amount, and the payment method.
After payment information has been entered and processed, the gift card should be available for use for payment.