APA stands for the American Psychological Association.
The library has many different resources -- in print and electronically that may assist you in better understanding the APA style. Many APA Internet links are on this Subject Guide.
Directions for typing the Running head can be found under the FAQs tab at the top of the page.
These have been ranked by most used and ease of use. Rules as stated by the official APA Assn are linked toward the bottom.