Go on youtube, go type in michael phelps, watch and be amazed. look at how he pushes off the wall and how straight hes body is. your arms must be fully extended in order for you to get the full affect. study hes movements and try your best to copy him
Start by doing the body roll underwater then keep your legs together. While your arms are to your side, roll your head up then let your body follow. You can go to http://www.wikihow.com/Dolphin-Kick for tips and a video.