Format your paper and cite your sources according to the Publication Manual of the American Psychological Association. (Ask a reference librarian where it is located.) This manual is the definitive source. The official manual is not online, though APA does provide some guidance on its website:
http://www.apastyle.org/learn/faqs/index.aspx
Here is a helpful guide from The Purdue Online Writing lab at Purdue University:
http://owl.english.purdue.edu/owl/resource/560/01/
Tip: Please talk to your professor if you have questions about how to cite your sources.