Go to System → Settings → General
Enter Google Analytics Account Number to enable.
Google Analytics is powerful, easy-to-use reporting platform lets you measure sales and conversions, but also gives you fresh insights into how visitors use your site, how they arrived on your site and how you can keep them coming back. Easy connect GA - add your Google Analytics Account Number to enable site activity tracking.
This also enables basic e-commerce activity tracking. You must enable e-commerce tracking in Google on the profile settings page for your website.