Login to Darwin's Dashboard and visit "Tracking Code" in the navigation.
Copy the tracking code HTML that you'll find there.
Login to the Joomla admin panel and go to "Extensions > Templates > Templates".
Click on the title of the template your site is using.
Locate and open the file that contains the
<head> tag, usually the
<head> tag might be in a different file other than
index.php in your theme. If in doubt, consult the documentation of your theme, or contact the theme creator.
Add the tracking code in this file before
</head> closing tag and save changes.
Once you've saved your changes, you can verify your install on the Darwin dashboard.