You have three slots that every 24 hours will roll new powers; they can range from being very weak to decently strong, and every six days you gain 15 charges. For the cost of one charge, you can use it to re-roll a single power, and you can use two charges to determine either how powerful the power will be or what type of power it will be, or you can use three charges to determine both how powerful it will be and what type of power it will be, though that can only be done once per power slot every six days.