Google Webmaster Tools is a no-charge web service by Google for webmasters. It allows webmasters to check indexing status and optimize visibility of their websites. It has tools that let webmasters:
Submit and check a sitemap
Check and set the crawl rate, and view statistics about how Googlebot accesses a particular site
Generate and check a robots.txt file
List internal and external pages that link to the site
See a list of broken links for the site
See what keyword searches on Google led to the site being listed in the search engine results pages and the click through rates of such listings
View statistics about how Google indexes the site, and if it found any errors while doing it
Set a preferred domain (for example, prefer example.com over www.example.com or vice versa), which determines how the site URL is displayed in search engine results pages
Set up a Google Account
If you already have a Google account, proceed to the next step. If you do not have a Google account, go to http://google.com and click on the +You link at the top of the page. Follow the on-screen instructions to create your account.
Set up a Google Webmaster Tools (GWT) Account
To set up Webmaster Tools, go to http://www.google.com/webmasters/tools and sign in with your Google account (If you have a Google Analytics account, you should use the same account).
On the main page, enter your site URL and click Add A Site. Once you have added your site, you need to verify that the URL you added is owned by you. Choose from one of the options to verify your site. Once you have verified your site, your account should be authorized and ready to use. Though, when you are setting up Webmaster Tools for the first time, it may take a few days for data to appear.