Each user can generate unlimited amount of gift cards but you can use only one free code per iTunes account. This means that you can generate more cards and gift them to your friends as well! The promotion is powered by RareSoftware.org. Read more here.
How to Activate iTunes Gift Cards
From your computer, iPad, iPhone, or iPod touch, just follow the App Store or iTunes instructions. You can also redeem by taking a photo of the PIN code using the camera on your Mac or iOS device.