Sometimes, it feels as though citing research within your paper is as hard as conducting the research itself, particularly when you are dealing with a source like a journal article that has multiple components. To make things even trickier, each major style has slightly different rules.
Write the citation information -- the author's last name and page number -- inside of the parentheses, but insert any end punctuation afterward, for example: (Thompson 138). If you include the name of the author in the sentence, omit if from within the parentheses, as follows: Thompson attributes this to socioeconomic causes (138).
American Psychological Association
Write the author or authors' last names followed by the year of publication and the specific page number you are citing, separating each by a comma. If there are multiple authors, use an ampersand rather than "and," for example: (Thompson, 2013, 138) or (MacNeill & Lang, 2000, 124).
Modern Language Association and Harvard
For MLA format, write the author or authors' last names, using "and" rather than an ampersand for multiple authors, and follow with the page number: (Thompson 138) or (MacNeill and Lang 124). Harvard format uses almost exactly the same rule, but with an ampersand instead of "and": (Thompson 138) or (MacNeill & Lang 124).