Submitting a Sitemap to the search engines is the quickest way to introduce yourself. If you simple build a website no one will know that site exists unless you tell someone.
Then that someone tells someone and if you have something interesting, the information gets passed along. The same with websites. You need to tell people it exists and the search engines want you to tell them where all your content is. By way of a Sitemap, you tell the search engines all about ALL the pages on your website and you tell them what pages you want them to "crawl" and what pages shouldn’t be included, if any.
NOTE: if you don’t submit a sitemap, the only way a search engine is going to find your website is from a link to your site from another site that the search engine robot has visited. When the robot goes to a site it processes all the information on that page including all the links to other pages on their website and outbound links to other websites. The robots then follow those pathways to the other websites and once on your site, the robots will then follow all the links around your site until they have indexed all you pages.
By submitting a sitemap, you are giving the robots the information you want about your site making their job simpler and improving your SEO ranking.
When creating a Sitemap you have to follow a certain protocol. At the time of writing this article Sitemaps needed to adhere to Sitemap protocol 0.9 to comply with all search engines. (http://www.sitemaps.org/protocol.html)
With Joomla there are several free sitemap generators. We typically use XMAP. If you’d like us to create your sitemap and submit it to Google on your behalf please simply contact us using this form it will take us approximately 30 minutes to establish the sitemap and ensure it is submitted through webmaster tools.
If you’d like to do it yourself, here are the steps.
You can test the validity of the sitemap here: http://www.w3.org/2001/03/webdata/xsv