Citations document information sources used in academic research, and they serve as an "address" of sorts. Regardless of the format/style you're using (APA, MLA, SBL, AMS, ACS, CSE, or others), they usually take two forms within the same work: Reference or complete citations, and shorter in-text or parenthetical citations (sometimes also called "author-date" citations) that correspond to the reference citations.
Examples of reference citations and their corresponding in-text counterparts:
A citation for a book (using APA Style):
A citation for an article in print form (using MLA Style, 8th ed., which represents a change in format from the 7th edition):
Usually, reference or complete citations that appear in References (APA style) or Works Cited (in MLA style) lists include at least several of the following elements:
For Articles in Magazines, Journals, & Newspapers:
APA and MLA Styles differ to some extent in what their in-text citations contain. But in both styles, the in-text citations include briefer information and refer you to the reference citations for more complete information. Every in-text citation must point to a more complete reference citation in a References or Works Cited page at the end--no "Lone Ranger" in-text citations are allowed!