Insert in google a keyword as sitemap generator and you will find a good tool. normally it is preferable. xml-sitemaps.com This tool will create your sitemap page and you have to download and then upload on your root website file.
Search Engines has crawlers, these are called bots. Robots.txt will specify if that crawler is allowed to crawl the page or not. you can set few private directories to disallow and crawlers dont crawl them. sitemaps are the maps , that tells crawler that you have so and so pages in the website.
thanks for your reply..kindly i want to knw thorugh robots.txt file crawler ll not crawl whole page or a section of page. n pls explain in detail what is included in sitemap file.
If you don't have much time to understand how it works, just head over to labnol.org and search for the term "submit google sitemap" with in the site. There is a detailed post with a video showing how to do this. You can use their free tool to construct a sitemap.