In a typical "ponzi" the new users pay for the earning of the older ones, on this plataform you only have to write and share content with users to get paid, there are 3 types of currencies. You have SBD (steem backed dollars) with are worth about 1$ of steem. Steem, which is the official cryptocurrency, and SteemPower, it gives your votes weight, the more you havem the more people earn from your votes