Use the claim link in the gift card email. When you are signed in, the card is added to your wallet as the page opens. If you are signed out, sign in or create an account first, and the card is added when you come back to the page.
Without the email, open the claim page at naayya.com/claim-gift-card, enter the Gift Card Code (it looks like GC-XXXX-XXXX), and select Look Up Gift Card. When you are signed in, the card is added to your wallet right after the lookup. If it cannot be added, the page says why and keeps Claim Gift Card so you can try again. If you are signed out, sign in or create an account after the lookup, and the card is added when you come back.
If Wallet is in your account menu, Claim at the top of the page opens the same claim page. On Overview, Claim it under What you have opens it too, with or without a balance.
You can also claim a gift card while you pay, without leaving checkout. Select Apply gift card or promo code, enter the code, and select Apply. The card is added to your wallet, and where wallet balance can pay for that purchase, it is used toward the total. You need to be signed in to apply a gift card.
After the gift card is claimed, its remaining balance appears in your wallet. If you cannot claim it, check that the code has not already been claimed, expired, or cancelled.