To manage Google Analytics settings for your Drupal site, 
Hover Configuration > System > Google Analytics

In the GENERAL SETTINGS section at the top of the configuration screen that appears, input your Google Analytics property ID.  It should start with "UA-".  For basic Analytics tracking, this should suffice.

Optionally, you can enable more detailed tracking for specific pages, by user roles, and more through the various tabs under TRACKING SCOPE.

Click Save Configuration to save all settings.