there are many programs and plugins available to generate the sitemap for your blog. to find a solution just search for "sitemap program" or "sitemap plugin (enter your blog software)". depending on which solution you pick it may regularly autogenerate the sitemap or you may need to manually do it.
sitemaps can be an xml or txt file. they help the search engines become aware of your content. they do not improve search engine rankings. to help search engines discover your content it is helpful to interlink your pages and avoid using forms. good luck.