The main difference between Gold Coins and Fortune Coins is that the former can’t be redeemed for cash prizes. They are just a virtual currency that you buy to play the games on the website. Fortune Coins are added to your balance for free with certain Gold Coin purchases.
Fortune Coins can be redeemed for cash prizes, for each 100 Fortune Coins you redeem you will receive $1 (subject to a minimum balance). Each Fortune Coin received must be used in-game at least once before it is eligible for redemption.