Free-to-play is a way of building games (a game model)that allows all players to experience the full game without having to purchase anything. There are optional in-game purchases if you would like to progress faster, but you can complete everything on your own. We use an energy system to regulate the number of levels you can play in one sitting, and there are diamonds, hearts, stars and many other things to help you progress(see the separate FAQs about these subjects for more information)