Click on the shopping cart icon in the top right corner and then click "Proceed to Checkout."
Choose the amount you want to put on the gift card. Common options include $15, $25, $50, and $100.
If you chose a digital card, you'll receive an email with the gift card code shortly after your purchase. If you chose a physical card, it will be shipped to the address you provided. Important things to keep in mind:
You'll see both digital and physical iTunes gift cards. Digital cards are delivered via email, while physical cards are mailed to you. Select the one that best suits your needs.