I've been using Google web analytic for years but not paying attention to it. Well, after reading this article Web Analytics Demystified by Avinash Kaushik (thanks to Steve M of SimplyGeo.com for the link) it gave me ways to understand my visitors and concentrate on their specific needs. I suggest that you read the article too if you want to improve your website contents and increase revenue.
The Google Web Analytics is free to use, so go there and register for your website. You can assign analytic code to each of your websites so you can track each visits, page views, bounce rate, etc.
Enough said, I already provided some reading links for you. Check them and don't be lazy (^_^).