By opening your Google Webmaster Tools and registering your Joomla sitemap, you will be able to know a wide range of information from your Joomla website.
Things you can learn with Google Webmaster Tools.
1. 404 errors.
2. How many pages have been indexed by Google.
3. General indexability problems.
4. Keywords driving traffic to your site.
5. Select the URL to display inside the search results.