First, click the Login Rewards button located at the top right of your screen.
Next, select the Codes tab, input your gift code, and click the Use button. You will then receive the following items:
1) 50 Stamina
2) 50 Honor
3) 100,000 Gold
4) Full Sets of Runes x10
5) Lvl. 2 HP Gem Scroll
6) Lvl. 2 PDEF Gem Scroll
7) Lvl. 1 DMG RES Gem
8) Lvl. 1 SDEF Gem
Notes: Promo codes may only be used once per server. Rewards obtained from the gift code are bound, and will be delivered directly to your backpack.