Citations document information sources used in academic research, and they serve as an "address" of sorts to those sources. 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, 7th ed.):
Livermore, J. B., & Quigley, E. (2002). Field assessment in crisis counseling (2nd ed.). Sage.
(Livermore & Quigley, 2002)
A citation for an article in print form (using MLA style, 8th ed.):
Piper, Andrew. "Rethinking the Print Object: Goethe and the Book of Everything." PMLA, vol. 121, no. 1, Jan. 2006, pp.
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!