Follow the author/date format as you would for a print resource. If you are citing a direct quote and there is no page number, use the name of the chapter or heading where the quote appears.
(American Psychological Association, 2010, pp. 171-172)
If you are referring to a website in its entirety, just refer to the name and website’s homepage address in the text of your paper. There is no need for a reference list entry.