Let's say there are results of an original study by Denton et al. that you want to cite, but you read about these study results in a book by Beaujot & Kerr. Ideally, you should try to find the original study by Denton et al. and quote or paraphrase from it directly. However, if it is not possible to find or to read Denton et al.'s, you need to do the following:
In the reference list, provide the citation of the source YOU are using, i.e. the book by Beaujot & Kerr::
Beaujot, R., & Kerr, D. (Eds.). (2007). The changing face of Canada: Essential readings in population. Canadian Scholars’ Press.
In text citation: name the original source and provide a citation for the source YOU use, for example:
According to Denton et al., ....... (as cited in Beaujot & Kerr, 2007).
One study found .... (Denton et al., as cited in Beaujot & Kerr, 2007).
Denton et al. (as cited in Beaujot & Kerr, 2007) found that ....
When you are quoting something and the quote contains a citation within the quote, you can just cite as usual. The reason is that it would not really be possible to use the "cited in" structure. Here is an example:
Actors "are encouraged to become immersed in a character's life (Stanislavski, 1950), an activity that calls for absorption" (Panero et al., 2016, p. 234).
In the above example you are quoting the entire portion that is in red, which consists of:
You are taking this quote from your source, which is Panero et al.
However, if you were to only use the first part, i.e. "are encouraged to become immersed in a character's life", then you would use the cited in structure as you would only be citing what Stanislavski said:
According to Stanislavski, actors "are encouraged to become immersed in a character's life" (as cited in Panero et al., 2016, p. 234).
Actors are "encouraged to become immersed in a character's life" (Stanislavski; as cited in Panero et al. 2016, p. 234).
In your reference list, you would again put your source, i.e. Panero et al.