There are several ways to flavor sugar for cotton candy. The quickest is to mix floss sugar concentrate with the sugar. Every other method requires time for the flavor to disperse and the sugar to dry.
Cotton candy is most easily made with a cotton candy machine. The machine heats the sugar until it melts, then spins, throwing the melted sugar against the sides of the machine, making the distinctive shape. Floss sugar concentrate is specifically made to be mixed with sugar for use with cotton candy machines. Other flavoring methods involve sealing a flavoring in with the sugar until the sugar is flavored and completely dry. The flavoring can be fruit peels, candy oils or flavoring oils.