Read this guide online at: http://mailchimp.com/resources/guides/understanding-reports/
Now that you've imported your list, created a campaign and sent it to your subscribers, it's time to sit back, relax and watch your reports come in. This guide will help you understand MailChimp's powerful reporting features and explain how to use them to improve your campaigns going forward.
An overview of MailChimp's reporting features, including:
Tracking opens and clicks
What the stats mean
Subscriber activity reports