There is no certification to coach volleyball. You do need to learn the rules, and it is often mandatory that you take classes to learn to officiate in order to coach. Best way to become a coach is to hook up with a club team and be an assistant. From there learn the ropes: the game, the drills, the other coaches, the players. If you have the skills people will recognize it. There are a lot of age group clubs in Hawaii. If you are not familiar with any of them, see a high school coach or check out some games.