To activate an iTunes Gift Card that you purchased at Uquid, you will need to have your iTunes app (If you don't have an account, it can be created on this link here) and follow these steps:
Step 1: Launch the iTunes application and log in to your account.
Step 2: From the menu bar at the top of the iTunes window, choose “Account”, then choose “Redeem”.
Step 3: Enter the code you have received from Uquid and click on the “Redeem” button.
Step 4: The funds have been added to your iTunes account. You can use the balance now!