In the seventh edition of the APA style, it is no longer necessary to insert "Retrieved from" before URLs.
Lastname, F. M. (Year) Title of document [Format if not a basic web page]. Retrieved from Site Name: http://xxxxxx
American Psychological Association. (n.d.) Protecting your privacy: Understanding confidentiality. http://www.apa.org/helpcenter/confidentiality.aspx
Websites rarely provide all the elements of a full citation. Refer to p. 3 of the APA Style Guide to Electronic References to see how to format a citation with missing elements. The "Site Name" in "Retrieved from Site Name" is only necessary if it is not clear from the author or the URL.
Kidron, Y & Lindsay, J. (2014). The effects of increased learning time on student academic and nonacademic outcomes: Findings from a meta-analytic review. (REL 2014015). Retrieved from Institute of Education Sciences website: https://ies.ed.gov/pubsearch/pubsinfo.asp?pubid=REL2014015
Include a report number after the title if provided. For reports with no authors named, the issuing agency can be provided as the author.
Bates College. (2016, March 3). Bates' Digital and Computational Studies Program will allow students to ask "the critical question of the liberal arts," says Margaret Imber, associate professor of classical and medieval studies [Facebook status update]. Retrieved from https://www.facebook.com/batescollege/videos/10153897132720822/
Francis. [Pontifex] (2016, February 17). Earnings and capital are not more important than the human person, but should be at the service of the common good [Tweet]. Retrieved from https://twitter.com/Pontifex/status/700061550275649536
Refer to pp. 32-34 of the APA Style Guide to Electronic References for further details.