A secondary source is an indirect quote, i.e. a source quoted within another source. Cite a secondary source only when you have not actually examined or used the original source.
If Smith is cited in a book by Blackwell and you did not read Smith's original work, list the Blackwell reference in the References list. In text, use the following citation:
Smith's research (as cited in Blackwell, 2018) supports claims that sleep deprivation has an impact on cognitive performance.
Jones is one of the speakers in a 44 minute documentary video written by Smith and directed by Ma. List the Smith and Ma reference in the References list. In text, use the following citation, including the start time of the quote in minutes and seconds:
Jones (as cited in Smith & Ma, 2016, 5:10) states that babies form memories early in life.