How can I use this?
Secondary Sources are useful for both gaining a broad knowledge of a topic area (e.g review papers), and for understanding how certain discoveries or projects were received by the scholarly community. They give you opinions, analysis, and a discussion of impact which you can use to place primary sources in context.
What is Secondary literature?
When other writers summarize or review the theories and results of original scientific research, their publications are known as Secondary Literature. These publication types serve to synthesize the findings to date and present the ideas to a wider audience. Examples of secondary literature include:
Insulin: Discussing the experiment and finding papers
Grodsky (1970) wrote a journal article called Insulin and the pancreas  in which he reviewed over 500 other publications about insulin.
Researchers typically use online indexes to find articles on a specific topic. If you searched in Web of Science and looked up the author "Banting, F", you would find citations to the articles he published in the Journal of Laboratory and Clinical Medicine. The "Finding Articles" module explains how to select and use an index.
 Grodsky, G.M. 1970. Insulin and the pancreas. Vitamins & Hormones, 28: 37-101.