This is the original text in the source* you want to use:
A central theme of Tan’s stories is the conflict faced by Chinese Americans who find themselves alienated both from their American milieu and from their Chinese parents and heritage.
Using the same words in your essay without quotation marks is plagiarism. Your reader does not know that someone else's words are being used--even if the work is cited. This is an example of what not to do:
A central theme of Tan’s stories is the conflict faced by Chinese Americans who find themselves alienated both from their American milieu and from their Chinese parents and heritage (Stein 2280).
If you do not make clear with quotation marks when you are using the exact words of an author, you are committing plagiarism--even if you credit the author in the bibliography or reference list. This is how you should use quotation marks to identify language that isn't your own:
Karen Stein argues that a "central theme of Tan’s stories is the conflict faced by Chinese Americans who find themselves alienated both from their American milieu and from their Chinese parents and heritage" (2280).
* Stein, Karen F. “Amy Tan.” Critical Survey of Short Fiction, edited by Charles E. May, 2nd rev. ed., vol. 6, Salem Press, 2001, pp. 2279-2282.
