This is a pretty common question that we get from clients a lot. Some people do not understand how creating a Google sitemap can benefit their search engine optimization marketing plan, but I feel that it is invaluable. Your Google Sitemap is a roadmap that Google follows to know how to index the pages on the site the proper way. Done effectively, which basically means done correctly, allows you the power of telling the search engines how to properly list your site.
To create a Google Sitemap, you will need a free Google account. Once you have an account, you want to log into the Google Webmaster Tools homepage (http://www.google.com/webmasters/tools). Once you are logged in, you want to click the Add Site button. Type your Website URL in the box and verify your site. You have alternate methods to verify your site. You can upload an HTML file (given to you by Google) to your site or add a META tag to your site.
Select the Sitemaps tab on the left and click Add General Sitemap. Type sitemap.xml after your website address and submit. The amount of time that it takes for your Google Sitemap to be registered varies, but should be done in 24 hours at the latest.
After that, you should monitor the number of pages that your site had indexed previously and watch the number climb.