If you have found (or been given) a book or article that is very relevant for your topic, review the list of references (the resources used by the authors). Some of these cited works may be helpful to you also. To find cited books or articles, where you look depends on what it is:
Is it a book (or book chapter or government document or videorecording)?
Is it an article (in a journal, magazine, or newspaper)?
To try to find items in a reference list you've found, you need to know if the reference is to a book or an article. How can you tell from the citation?
BOOK (note place & name of publisher)
Bagdikian, B. (1977). The media monopoly. Boston, MA: Beacon Press.
ARTICLE (note volume & page numbers)
Chambers, T. (2001). Losing owners: Deregulation and small radio markets. Journal of Radio Studies, 8, 292–315.
BOOK CHAPTER (note place & name of publisher, plus the word "In")
[NOTE: In this example, the first title is the CHAPTER title, which is "In" the BOOK title.]
McDowell, S. D. (2000). Globalization, local governance and the United States Telecommunications Act of 1996. In J. Wheeler, Y. Aoyama, & B. Warf (Eds.), Cities in the telecommunications age: The fracturing of geographies (pp. 112–29). London and New York: Routledge.