APA format refers to the formatting style described in the American Psychological Association (APA) publication manual. It is essentially a list of "rules" that people can follow when writing a research report or essay. These rules vary from the size of the margins, type and size of font, the way headings are given, to how to write statistical results. By following APA format, it ensures that everyone can use a consistent style in writing their documents, whether they be research reports, essays, literature reviews, or anything else. The APA manual is used widely. You will see it being used in not only psychology, but also in criminology, education, humanities, and human services to name a few disciplines.
In the majority of cases when writing your assignment, you should use APA format. There are some exceptions to the strict form of APA format as given in the publication manual. The major ones include the format and content of the title page and that figures and tables should be presented within the document (not right at the end). In general, if you follow the guidelines in REDBOOK for your assignment, you will be fine.
The following pages give further information on correct use of APA format.