First select the page in this site where you want to cite. There are ways in citing this site based on APA format. This site contains facts from the study guides or lesson plan. Usually, they have authors. Other information written has authors, the tutors or the students who have added some information regarding a particular question or topic.
Consider this example:
1. If you are going to cite this particular lesson guide, http://www.enotes.com/topics/public-health-nursing, you can click the link that allows you to create a reference for the page.
"Public Health Nursing" Encyclopedia of Public Health Ed. Lester Breslow. Vol. 3. Gale Cengage 2002 eNotes.com 28 Oct, 2013 <http://www.enotes.com/topics/public-health-nursing/reference#reference-public-health-nursing>
2. If you are going to cite a comment or an answer, http://www.enotes.com/homework-help/write-letter-athe-nursing-times-describing-435725, this can be cited as follows:
[karythkara]. (2013, May 20). The Nursing Times (NursingTimes.net) is a sophisticated publication that advocates for ethical responsibility in medical care[Enotes answer]. Retrieved from http://www.enotes.com/homework-help/write-letter-athe-nursing-times-describing-435725.