Sitemaps can help Google with discovering all the pages of your website. To submit it to Google, follow these steps.
First, you must have a Google Webmaster Tools account. If you have one then you can skip this step and go on to the next one.
Second, go to http://www.google.com/webmasters/tools. This will take you to the Webmaster Tools dashboard.
Third, select your website from the list. You will see a page that shows keywords, links, and other data. Under keywords, you will see Sitemaps. Then click on Submit a Sitemap.