Just send the following steps to your friend:
1) Make sure the latest version of iTunes is installed on your computer. The latest version is available free of charge from the Apple website:
2) Click the following link to launch iTunes and display the Redeem page:
Note: If this link doesn't work for you, simply open up the iTunes application, click iTunes Store on the left, and when the iTunes Store homepage loads, click the "Redeem" link in the upper-right corner of the page.
3) Enter your 12-digit gift code and click the Submit button.
4) A message will appear confirming that your gift code has been redeemed. If you don't have an account, you can create one at this time.
hope this will work