According to Hacker and Sommers, when source material [a quotation, summary, or paraphrase] is used, an in-text citation, which is "a combination of signal phrases and parenthetical references" is used (389).
The parenthetical citation or reference "comes after the cited material," "includes at least the page number" and is placed a the end of the sentence in which the source material appears so that the reader can locate the information in the original souce (389).
If the original source does not include page numbers, a paragraph number or section may be used. When the orginal source is a poem, a play, or a sacred text, the citation includes line numbers, act.scene.line numbers or chapter and verse, respectively.
In some circumstances the author's name or the title of the text may be included in the parenthetical citation.
The in-text citation has a corresponding bibliographic citation in the Works Cited. The information provided in the signal phrase and the parenthetical citation "match" an entry in the Works Cited, an alphabetical list of works that are referenced by in-text citations, thus "works cited."
For additional information and models of in-text citations, see Hacker & Sommers text (MLA-4a) or an online source like the OWL at Purdue, the on-line writing lab at Purdue University.