Butterfly needs both stamina and technique, but the body movements are not difficult because you will have done many of them before in other strokes. When racing butterfly, your arms must come out of the water on every stroke. They must not drag through the water when they move from your hips to the entry position. Follow along with this quick how-to animation to learn how to do the butterfly stroke for swimming.
Both of your arms work at the same time and keep moving throughout the stroke. Put your hands in the water in front of your shoulders and pull them towards your feet.
When your hands reach your thighs, lift them out of the water and throw them back to the start. You should keep your head in the water all the time, except when you need to breathe in. If you lift your head up at other times it will be almost impossible to get your arms over the water. The easiest way to breathe in is to push your chin forwards so that your mouth comes out of the water. It is best to do this when your arms are almost at your thighs.
The difficult part is getting everything in the right order, so:
1) Kick your legs down as your hands go in
2) Kick your legs down as your hands come out
3) Keep your head down when your arms go over the water
4) Keep your head down until your arms are near your thighs
5) Breathe in quickly