You will need to assemble all the content for your site before actually creating the site. This includes writing all the text describing your business, products or organization (including an overview for the main page, specific product descriptions, information or articles, order forms, etc.) ; finding graphics that illustrate those products or ideas (including logos, photos, drawings, illustrations, brochures, etc.); organizing other elements that you want to include (including sounds, videos, animations, etc.).
You may want to hire a writer or editor to help with the creation or polishing of the text. Graphics will have to be scanned or created by a graphic artist and then converted into gifs or jpegs. Sounds, videos and animations must be converted into an appropriate format for the web.