There are several approaches.
What has been taught for ages is the two kick per stroke style. Kick your hands in, kick your hands out. Some advocate kicking the hands out to be the stronger one, while others say the kick your hands in should be the stronger. I think the majority say the former.
Several years ago Terry worked on developing a model that would enable most swimmers to swim the Butterfly for distance. In this model which is laid out in his Buttlefly DVD the swimmer just uses one kick per stroke. That is kicking the hands in and emphasis on landing forward, not down. Many other fine points as well.
As in other strokes he has broken the stroke down and progresses the learner thru stages that facilitates the creation of a relatively tireless smooth stroke.
Hope you enjoy the ride. When one gets into the rythum it is a joy to experience.
May we swim with ease at the speeds we choose.