How do you redeem your nx cash

Log in to maplestory, then click the button that says Charge Account at the top right corner. Choose which option you need to use (Game Cards, Charge Online, Charge Mobile, Earn Free NX.) and then when you click which one you want to use it will either go to a different tab, or pop up a screen (in one browser). For game cards, it will ask you for the code on the back of the game card and you type it in. Press ok and your account will have NX.