https://www.facebook.com/help/390967410974308/?q=insights&sid=0n9P8AYs4wEucWWOL Insights provide measurements on your Page's performance. about your audience, and see how people are discovering and responding to your post . Adspace
Basically it is a Facebook's version of web page analysis, which allows a user to keep track of information such as Page View, Fan Statistics, Wall Posts and Photo Views etc.
this is a great guide that explains everything you can do with Facebook Insights http://www.fissionads.com/university/facebook-audience-insights-101/
Its a very useful tool, but its very limited, specially if you are trying to get insights from other countries.