Social Tagging consist of Social Tags, Note Board, Ratings and bookmarklets.
Social Tags and Note Board can be associated with pages, library, items and much more. We can add tags and notes by using "Tags and Notes" control in ribbon (Farm feature "Social Tags and Note Board Ribbon Controls") which also has privacy setting. All these activities are visible in My profile under "Tags and Notes" tab.
Rating are associated with library and list for which we need to activate "SharePoint Server Publishing Infrastructure" feature. Go to list settings -> Rating Settings -> Allow items in this list to be rated - Yes.