To cite your sources in APA, you first need to understand the anatomy of a citation.
An article citation might look this:
Author, A. A., Author, B. B., & Author, C. C. (Year). Title of article. Title of Periodical, volume number(issue number), pages.
Pickering, G. J. (2009). Optimizing the sensory characteristics and acceptance of canned cat food: Use of a human taste panel. Journal of Animal Physiology and Animal Nutrition, 93(1), 52-60.
A citation for a book might look like this:
Author, A. A. (Year of publication). Title of work: Capital letter also for subtitle. Location: Publisher.
Mayr, E. (1982). The growth of biological thought: Diversity, evolution and inheritance. Boston, MA: Harvard University Press
A citation for an article or chapter in an edited book might look like this:
Author, A. A., & Author, B. B. (Year of publication). Title of chapter. In A. A. Editor & B. B. Editor (Eds.), Title of book (pages of chapter). Location: Publisher.
O'Brien, C. (2005). Drug addiction and drug abuse. In L. B. Brunton, J. S. Lazo, & K. L. Parker (Eds.), Goodman & Gilman's The pharmacological basis of therapeutics (11th ed., pp.607-629). New York, NY: McGraw-Hill.
Different types of publications (articles, books, conference papers, book chapters, edited books, etc.) include different elements. The elements required for a particular type of citation are those that allow a reader to find the source you cited.
The Purdue OWL's APA guide is a comprehensive online guide to citing and formatting using the APA style.
The full Publication Manual of the American Psychological Association, 6th edition, is available in print at Cline Library at the Research/Help Desk.