These instructions assume that a Google Analytics account is set up, the Google Analytics Drupal module installed, and site search enabled on the site.
Open the Google Analytics configurations. On most sites this is found in the Site Configuration section of the admin menu. Scroll down to the advanced settings group and select the track internal search option.
Save your configuration settings and open your google analytics account.
Access the Analytics Settings link in the top left corner of your analytics account. Select edit under the actions column for the website you want to track search terms for.
Under the Main Website Profile Information you will see an item for Site Search. In the top right corner of this box select the edit link.
Select the Do Track Site Search option and enter the term search in the Query Parameter
You should now see the Do track site search enabled in the profile information.
Now access your site statistics from the View Reports link for your site. The site search statistics are found in the Content section. From this point on, you will be able to track the terms that users are entering to find content on your site.