These are just three or many citation formats used by researchers and authors. Be consistent and follow your instructor's guidelines when preparing your citations.
Most style manuals are not available in full-text online. The Library Reference Desk has a copy of the print manual available.
Microsoft Word, most subscription databases, and online resources such as EasyBib offer shortcuts to formatting in MLA, APA, Chicago and other sytles. However, these systems are NOT ALWAYS ACCURATE
If you use these online tools, it is important to double check the accuracy of your citations against the official citation rules for that style.