When you register on Zigiz you start out as a regular member. As a regular member you have access to the all basic features, like playing games for free and setting up your profile.
Gold members can do a lot more. Besides having access to all the features a regular member has, they also have access to all the paid jackpots and tournaments, allowing them to play for real money. As a gold member you also have access to more profile features and cool promotions.
You become a gold member by doing a payment in the Zigiz shop.