Including sitemap in your site is a very good practice from Search Engine point of view. However specifically you should include XML site map which provides an ease for search engines to crawl while HTML sitemap for visitors for easy navigation of your site. apart from this google crawls to your site content via different directories websites blogs articles social networks bookmarking sites etc etc
Surely Sitemap helps, And more than that Popular content that attracts linking from different sites, Blog etc also helps a lot.
yes submit xml sitemap in google webmaster tool help. moreover if you have backlinks from high pr website that'll also help...
Submit you sitemap to google webmaster tools. Google crawls your site using google bots or spiders...
First of create robots.txt and sitemap.xml and than create webmasters tools in the various search engines and submit your website sitemap.xml into them....