Gift cards can be delivered one of two ways- via email or via print at home.
If the gift giver chooses email delivery, the card is sent to you via email and it's immediately applied to your account.
If the gift giver chooses the print at home delivery, it means they want to give the gift card to you personally. You won't receive an email and the credit is not applied directly to your account. Once you receive the gift card, you can apply it to your account by going to Settings >Gift Card/Promos on the website or Menu > Registry > View Gift Cards/Promos on the iOS app.