The sites by Hacker and OWL offer guidance for the entire research and writing process, including APA style and formatting.
The other sites offer easy-to-use templates for generating APA citations.
Introduction to APA Documentation Style
Academic writing standards require you to credit all sources that you use to write a paper, report, or study. The America Psychological Association (APA) documentation style provides a guideline for properly crediting your sources by requiring notes in the text of your work that point the reader to an alphabetical list of your sources, called “references”. Properly citing your sources of information allows a reader to locate the original sources of information you used in your writing and will also help you avoid the serious offense of plagiarism.