REFERENCING is a way to demonstrate that you have extended your reading, learning and comprehension by using relevant and up to date sources.
Primary sources contain the original data and conclusions of the researchers who were involved in the experiments. These articles also contain details about how the experiments were done. Source
Secondary sources offer an analysis or a restatement of primary sources. They often attempt to describe or explain primary sources. An example of a secondary source in the sciences is a 'review article' that reviews several studies on the same topic. Source
CITATION is recognising resources in-text to support an argument/conclusion.
e.g in text citation
According to , the complexity of mechanical and electrical systems and applications of vibratory equipment in them have increased markedly in recent years.
 A. Brandon, “Vibration analysis resolves vibration equipment problems,” in Fundamental and Advanced Vibration Analysis. New York: Wiley, 2014, ch. 7, pp. 129–134.
To give recognition to the original author of the text, opinion, idea, fact, image, etc.
To enable your reader to check your information
Sources confirm the completeness of the research
Quotations and references lend authority to the argument, view, etc.
The source list can be consulted by the reader to verify information in the text
The sources can be used by the reader as additional sources to a topic. Source