MC_Will on "Using Template in wpMandrill"

All you need is a HTML container with an editable region called 'main':

<div mc:edit="main"></div>

This thread might help you understand Mandrill templates and Merge Vars and how to use them in wpMandrill:
http://wordpress.org/support/topic/understanding-wpmandrillmail?replies=6#post-4244274

Also, this KB article has interesting information on editable regions:
http://help.mandrill.com/entries/21694286-How-do-I-add-dynamic-content-using-editable-regions-in-my-template-