A Sitemap is a plan for your site that will be used by search engines to crawl your blog. It is important for a better ranking because blogs have countless pages and therefore the robots that go through it need help to navigate. The sitemap contains all URL’s of your articles, the last time that the blog has been updated, the update frequency and importance, based on the traffic generated and the number of comments. This is an XML file stored on the server, which is the same as your blog.
To create a Google sitemap, which Googlebot is the robot that will most often visit and crawl your blog, you just need to download a plugin, Google Sitemaps will take care to place the file in the right place for you. You only have to set the options according to your needs. Place it directly in the ROOT of your blog, www.yourblog.com/sitemap.xml.