One of the great ways in which eNotes is designed to help students is the addition of a specific citation button on most study guide and reference pages. This button will automatically generate the correct citation for your bibliography, as well as including the correct sourcing for any primary or secondary sources from which the page draws. This citation button is located below the title and study guide tabs, just above the text; it is to the right of the "print" and "pdf" buttons. Clicking it will open a new window with the properly-formatted citation.

For example, in your requested link, the page draws from the textbook Great Lives Through History, either quoting or paraphrasing information to create the text. The citation is therefore shown as follows:

"Augustus." Great Lives from History: The Ancient
     World, Prehistory-476. Ed. Christina A. Salowey and
     Frank Northen Magill. Salem Press, Inc., 2004.
     eNotes.com. 2 Oct, 2012
     <http://www.enotes.com/augustus-reference/>

Make sure you create a hanging indent by indenting the second and following lines of the citation (where they naturally break in your word processor, not where they appear here or elsewhere) five spaces or one Tab press. There are many other resources available for citing web pages around the Internet; the Citation Machine is one of the oldest, although it has trouble with eNotes. For most eNotes pages, using the "Cite" button will give you the best results, as long as you format it correctly afterwards. Check the OWL at Purdue link below, as well as the eNotes help guide on citation for more information.