Sitemap Help

I need to create an effective sitemap. I'd always been under the impression that a site map was just a well-organized page containing every link on a website. But now I see that there are XML site maps. I need to know: - Which is better for SEO? - Does the sitemap need to be submitted to the major search engines or will they just find it when they index the site next? - What exactly is an XML sitemap? - Are XML sitemaps viewable on the web? Or are they just files for the search engines? I'd like send a URL to a very small website to the person I hire for this project and have him build me an XML sitemap so I can study it and duplicate it for other sites in the future. And, of course, I'd like expert answers on the previous questions. Thank you!!