Sources you cite should be ones that you have actually examined in their original, complete form. A secondary sources is a source that cites the original work which you intend to use as a reference.
When you have to use a secondary source for some reason, give the secondary source in the reference list; in the text, name the original work and give a citation for the secondary source. For example, if Smith's work is cited in Blackwell and you did not read Smith's work, list the Blackwell reference in the reference list. In the text, use the following citation:
Smith's research (as cited in Blackwell, 2009)