You can use one secondary sources (book, article) four ways!

1. Go back in time: look at its footnotes and bibliography
2. Forward in time: do Cited By searching
3. Subjects: look for other sources with similar topics / subjects
4. Methods: look for other sources that use similar methods

"Cited By"

Works the cited a particular original work.

1. Search for a topic or work in Google Scholar
2. Click the "cited by" link under a relevant result
3. The resulting works will all cite the first work

"Related"

Works the cite many of the same things that a particular work cites.

1. Search for a topic or work in Google Scholar
2. Click the "Related Articles" link under a relevant result
3. The resulting works will cite one or more articles that the first work cited

Searching within a result list

1. 

   Checking the "search within citing items" box at the top of the result list and then entering a new search.