APA (American Psychological Association) style is used predominently in the social and behavioral sciences, and education. Many other styles (e.g. CBE, AMA) are modeled after, and default to, APA.
Currently in the 6th edition, the Publication Manual of the APA, is the authority on "how to write" and "how to cite". Most people use it to see how to put references in their papers (a.k.a. in-text citations) , and how to format a reference list.
Basically, in-text citations look like this
The mllitarization of police departments has risen steadily since 9/11 (Lusk, 2013).
The reference citation looks like this:
Lusk, R. (2013). Army tanks in your town. Journal of Police Trends, 6(3), 70-87. Retrieved from http://jsn.sagepub.com/
But, it can get very confusing. This tutorial from APA will help. These links give good examples:
MLA Handbook (Modern Language Association) includes the style used in the humanities and liberal arts (e.g. English, literature, art)
A parenthetical citation (in-text) looks like this:
The militarization of police departments has risen steadily since 9/11 (Lusk, 71).
The works cited (references) looks like this:
Lusk, Robert. "Army Tanks in Your Town." Journal of Police Trends 6.2 (2013): 70-87. Academic Search Complete. Web. 26 Aug. 2014.
MLA has lots of rules. This tutorial from OWL may help, and these links provide good examples:
The Library has a wonderful Citation Help guide to many different styles.
In addition, google the style you need, but make sure you are going to a reputable site. Whenever possible, try to get to the professional association which produces the style.
Many Library databases, and companies format citations for you, but think of them just as a way to get started.
Online generators can also make your job easier.
For more heavy lifting consider