Referencing guide
The Harvard style is a generic term for any style which contains author-date references in the text of the document, such as (Smith 1999). There will also be a list of references at the end of the document, arranged by authors' names and year of publication. There is no official manual of the Harvard style: it is just a generic term for the many styles which follow that format.
A guide for using that style and examples citing of different types of media can be found at http://www.library.uq.edu.au/training/citation/harvard_6.pdf
The APA style is the standard style used in Psychology, but it is also widely used in other disciplines, especially in the Social Sciences. It is one of the many variants of the Harvard style.
See http://www.library.uq.edu.au/training/citation/apa.pdf for a guide on using this system
The Vancouver style is a generic term for a style of referencing widely used in the health sciences, using a numbered reference list. There is no official manual of the Vancouver style, but the US National Library of Medicine's style guide is now considered the most authoritative manual on this type of referencing.
A guide for this type of referencing is at http://www.library.uq.edu.au/training/citation/vancouv.pdf
