I have to summarize a whole article. How do I cite it, if my whole assignment is about that?
When you summarize someone else's information, especially if you will be spending a lot of time summarizing (for instance, your assignment is to summarize an article or a chapter in a book), it is important to introduce your source right away.
Example: Stineway and Harper conducted an excellent experiment in late 2009 that is only now coming to full fruition. Their article, Hamsters Texting at the Wheel covers a whole variety of insights in the the driving habits of hamsters. Of note...
You will note that the introduction above includes more than just the standard APA in-text citation which would look like this: (Stineway & Harper, 2009). When introducing a source, rather than citing it, that is OK.
As you write your summary, you will want to remind your reader, occasionally, that you are still summarizing. You can do this simply be referring back to the authors, the title of the article, or both. Remember, however, that anything that needs an APA in-text citation will need to refer to author and date.
Example: According to Stineway and Harper (2009), hamsters are the best rodent drivers there are. They indicated in their literature review that gerbils are too distractable to be safe and that guinea pigs were too slow-reacting.
Note: Since you asked, a single citation at the end of the summary will not meet reference requirements for APA or any other citation style.
For more information on introducing and citing sources, see http://rasmussen.libanswers.com/faq/32328