A rookie butterflyer often get confused about the dolphin motion. The butterfly has only one dolphin per arm stroke, but two kicks. The first kick, is the large kick we see breaking the surface of the water on a proficient butterflyer and help drives us forward. The second, smaller kick is where the beginner often goes wrong. The second kick should be smaller and done as the arms are exiting the water. This smaller kick is a supporting kick meant to help you lift your head and arms out of the water.
Watch this underwater video of a butterfly race to see the two kick, one dolphin butterfly in action. Every swimmer in the video has two kicks per arm cycle, but only one breaks the surface of the water, the other, the supporting kick stays smaller and below the water.