Sitemaps have no standardized name or file location, so search engines do not read them by default. Instead you should notify the search engines about your sitemap. You can place a link to your Sitemap file in your robots.txt file, submit your Sitemap via the Webmaster Tools of Google and Bing or just submit your Sitemap with the Web CEO Sitemap Generator.
You may give your Sitemap file any name you choose and store it anywhere on your site (although the site root is a reasonable place to put it). The Sitemap file must be a UTF-8 encoded text file, that means that URLs with some special characters must use entity escaping for search engines to parse them correctly.