When you use quotation marks and credit the author and the work, you make it clear you are using someone else's words. Be careful when typing out the quoted material and not make any mistakes (inaccurate quotations are a sign of sloppiness but not necessarily plagiarism). There are many styles for giving credit. Check with your professor for the style you should use in your assignment.
One critic has argued 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” (Stein 2280).
You need to list the work in the bibliography or reference list. Check with your professor for the bibliographic form you should use in your assignment.
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.
The block quotation format is used when the quotation is long:
One critic has made the following claims about Tan's work:
A central theme of Tan’s stories is the conflict faced by Chinese Aumericans who find themselves alienated both from their American milieu and from their Chinese parents and heritage. Other themes include storytelling, memory, and the complex relationships between mother and daughter, husband and wife, and sisters. (Stein 2280)