Read this guide online: http://mailchimp.com/resources/guides/how-to-use-merge-tags/
MailChimp provides all kinds of merge tags to dynamically add content to your email. You can include something as simple as a subscriber’s first name, or create an entire campaign using nothing but merge tags. This guide is a step-by-step tutorial for using MailChimp’s merge tags.
Tips on how to include dynamic content in your email campaigns with merge tags for:
Formatting custom list information