Use secondary sources sparingly; you should always try to locate the original source of information which is cited in a work that you have read. This is not, however, always possible: sometimes the original work is out of print, unavailable through your usual sources or not available in English.
If you read an article or book which cites information that you want to cite; always refer to the source where you found the information, not the original source.
For example:
If you read an article by Alex Reid, in which he cites information from a previous study by Seidenberg and McClelland, and you wish to refer to this information in your assignment:
• You would acknowledge Seidenberg and McClelland in the text:
Seidenberg and McClelland’s study (as cited in Reid, 2007) found that the paranormal…
• In your reference list at the end of your assignment; your entry would be a reference for Reid's article because that is where you sourced the information:
Reid, A. S. (2007). Study of multiple paranormal phenomena. Journal of Abnormal Psychology, 45, 13-26.