SteamPunk is a fashion style that is derived from science fiction, but rather than science fiction that looks into the future steampunk is a retrospective style that tends to focus on whimsical world powered by steam where the mechanical revolution is in high rear and invention abounds.
The fashion of steampunk marries influences from both traditional Gothic attire and Cyber gear. Much steampunk styling revolves around the time period of the mechanical revolution, and hence there are often similar silhouettes as seen in traditional gothic, with corsetry, bustles, and petticoats for women. Mens steampunk fashion tends to lean toward that of the explorer and inventor, imagine what a man might have worn on safari at this time? Now add sci-fi elements (much like you might expect with cyber) with a bronze and brass retro flare. Of course this is only touches on what is steampunk, but it should be enough to help you navigate the styles listed and gain an insight into why you should add them to you wardrobe.