Google Analytics is a powerful and free web analytics tool that is used by many website operators. You can learn more about Google Analytics here: http://www.google.com/analytics/
One of the nice features of Google Analytics is that it can show you where your traffic is coming from. Furthermore, if you have setup specific goals within Google Analytics (such as "making a purchase") it can show you which traffic sources lead to conversions.
By default, Google Analytics will automatically track all traffic from search engines, social networks and your AdWords account. But, Google Analytics will also let you track custom campaigns through a process known as "link tagging". You can learn more about how to tag your links here: http://support.google.com/analytics/bin/answer.py?hl=en&answer=1033867
To make things easier (and faster!), Elite Email can automatically tag your links so that you do not have to do anything special. When this is enabled, you will be able to login to Google Analytics and view incoming traffic from your email campaigns in addition to seeing how many of those lead to conversions. Furthermore, you can even drill down to a specific email that you sent to see the results it produced.
You can always view opens and clicks from the Reports section of your Elite Email account, but by integrating with Google Analyitcs you can get deeper insight into what people did after they clicked.
To enable Google Analytics tracking, simply check the box on your Email Settings page and identify your specific email with a campaign name that will later show up in Google Analytics.
Read more about this integration on the Elite Email blog.