When you are referring to the works of others in your essay, you will use what MLA calls parenthetical citations. Parenthetical citations consist of sufficient information to recognize each source, usually author's name and page number, placed in parentheses after your paraphrase or direct quote from the source.
The Online Writing Lab (OWL) at Purdue University has a helpful page on MLA in-text citation. Here is an example of a parenthetical Author-Page citation:
Two University of Chicago palaeontologists had devised a test for species extinctions; according to them, mass extinctions were quantitatively and qualitatively different from regular extinction events (Benton 137).
Remember that every source mentioned in the text of your essay must have a corresponding full citation on the Works Cited page.
The book by Benton used above would have this Works Cited entry:
Benton, Michael J. When Life Nearly Died: The Greatest Mass Extinction of all Time. London: Thames & Hudson, 2015. Print.
Here is more OWL Purdue information on how to cite other types of sources on your Works Cited page: