Google Analytics is a free, web analytics tool that is hosted by Google.
Google Analytics shows you how visitors actually find and use your site, so you will be able to

1. make informed site design and content decisions
2. improve your site to convert more visitors into customers
3. track the performance of your keywords, banner ads, and other marketing campaigns.
4. and track metrics such as revenue, average order value, and ecommerce conversion rates.

Google Analytics can help you answer important questions about your site and your marketing initiatives, such as

1. How are visitors using my site?
2. How can I make my marketing campaigns more effective and accountable?
3. Is my content effective?
4. Where are visitors abandoning their shopping carts and where do they go afterwards?
5. How can I improve my site navigation and help my visitors get more out of the site?

Google Analytics has been designed to meet the needs of novice users as well as web analytics experts.Some of the features include:

1. Map Overlay which can help you understand how to best target campaigns by geographic region
2. AdWords Integration which makes it easy to track AdWords campaigns and allows you to use Google Analytics from your AdWords interface
3. Internal Site Search which allows you to track how people use the search box on your site
4. Funnel Visualization so that you can optimize your checkout and conversion click-paths