If you have purchased a Game Time Card, you will need to apply it to your NC Account.
First, log in to your account here: https://login.ncsoft.com/login
Click on 'Apply a Code',
Enter the serial number printed on your Game Time Card, and click on ‘Activate’.
Additionally, game time cards can be exchanged for NCoin which is used by Blade & Soul, Lineage II and Aion*. For more information about NCoin, and how to use your game time cards to buy NCoin, click here.
*Aion uses Black Cloud Coin but still allows in-game conversion of NCoin to Black Cloud Coin. This exchange is a one-way conversion, meaning you cannot convert Black Cloud Coin to NCoin.