The Social Engagement reports in Google Analytics allow you to see how people shared content on your site via social actions. Examples of social actions on your site that can be tracked include Google +1 button clicks, Facebook "Like" and "Send" interactions, and http://del.icio.us/ bookmarks.
Your reports automatically include information on any Google +1 interactions that occur on your site. To track interactions with non-Google interactions, you will need to modify your tracking code. More information.