When you include information from a source in a paper, presentation, or other project, you must give credit to the source's author. (You do not have to cite information that is common knowledge, such as that the U.S. has 50 states.) Some definitions:
Things to include when quoting or paraphrasing a source:
You may be analyzing the source material, relating it to your own ideas, critiquing it, using it as evidence to back up a claim, or referring to it as an example of a broader idea.
Your writing is what gives the source material context and meaning for your reader. If you just drop in quotes and paraphrases, that's like tossing someone a handful of chocolate chips when they asked for a great cookie.
What is a citation?
The act of telling your reader where you got your information is called citing your source.
The information you share when you cite a source is called a citation, or sometimes a reference.
There are two kinds of citation:
(1) a short little tag that appears in the main text of the article, essay, or book ("in text"), and
(2) a much more detailed citation that comes in a list at the end of the article, essay, or book (called a "reference list" or "works cited list" or "bibliography")
Readers look at the short in-text citation and then if they want more information, they look up the rest of the information in the longer list at the end.
These are short so that they don't interrupt the flow of reading. The exact rules vary according to citation style (see below), but the in-text citation typically contains just the author's name and date of publication, sometimes with a page number. (Sometimes it is just a number - when it is a number, it is called a footnote or endnote number.)
Example of in-text citation in APA style:
According to Smith (2015), NYC pizza was ranked the most foldable kind of pizza by 999 pizza-eaters.
As a reader, you would now have enough information from this in-text citation to look at my list of references to find more information about where Smith provided this information in 2015 - it could be a book, article, video, interview, or any other source.
What the matching end-of-work citation would look like:
Smith, B. (2015). "Survey of pizza-folders and their preferences". Journal of Pizzaology, 2(6), 16-20.
This longer citation shows me:
What is a citation style? Different disciplines use slightly different formats for their citations. For example, scholars who write about literature usually use MLA style; psychologists and other social scientists use APA style, and historians usually use Chicago style. The following pages addresss specific questions about citing in APA, MLA, or Chicago style, or see the Purdue OWL website (from Purdue University), which includes many more detailed rules for several styles of citation, including AMA (American Medical Assocation).