If its Wordpress than you can use these plugins http://wordpress.org/extend/plugins/search.php?q=sitemap I Recommend From Them http://wordpress.org/extend/plugins/bwp-google-xml-sitemaps/
If you are using Wordpress, then I would suggest to use "Google Sitemap Generator" plugin. You can find it in Wordpress repository.
Like others have said you can use Wordpress plugins. Also make sure you report it to Google "Webmaster Tools". For Blogger you can report your XML to Google like here:
You can create your sitemap manually. there are a number of third-party tools that can help you generate Sitemaps. sitemap generator that creates XML and HTML variants. You can create sitemap here- http://www.xml-sitemaps.com/