Websearch. Here on Instructables, and on the Web as a whole. You will find definitions (not all of which agree) and examples (not all of which are agreed to be steampunk).Basically, it's an aesthetic inspired by the past's future that never was. Cross Victorian culture (usually, but not always, British Empire) and the sciences and engineering of the time with "mad scientist" and you're pretty much there. Lots of exposed, finely crafted, ornamented machinery which is at least plausible by the science fiction of that time. Costumes and roleplay appropriate thereunto.You create steampunk jewelry and clothing... by creating jewelry and clothing which would be suitable for people living in this retro-technological fantasy world. What would a Victorian "renaissance man" -- or woman -- be wearing while exploring the cannibal islands with pith helmet and raygun and klunky steam-powered robot? Or when working in the home laboratory, or in the factory building, to create the device which will take men through the aether to another planet? Or when telling others of the latest expedition which will attempt to bring back a living dinosaur for Her Majesty's zoological gardens (and how he barely got home alive from the last one)?