1.  “But in spite of that vicious-circle relationship for all individuals when taken together as the whole body of producers and customers, each person in our present industrial system is striving to make money.”

This is a sentence from a book, it is primary source.

Reference:

Joseph E. Shafer, (1928). An Explanation of the Business Cycle. The American Economic Review, Vol. 18, No. 4, pp.619.

Retrieved from http://www.jstor.org.proxygw.wrlc.org/stable/1810445?seq=3

2.  “Mr. Shafer's discussion of the business cycle in the December, 1928, number of this journal contains a section on the equation of exchange. He starts out wisely by defining his concept of the various terms in Professor Fisher's familiar form of the equation: MV + M'V' = PT.”

This is a citation from an article, which is a secondary source. 

Reference:

Caroline Whitney, (1929). Mr. Shafer on the Equation of Exchange and the Business Cycle, pp.76.

Retrieved from

http://www.jstor.org.proxygw.wrlc.org/stable/view/1809586

3.  A bibliography (not listed) of a book, it is a tertiary source.

Reference:

William D. Wells (1971), "Factor analysis in marketing research,” Faculty working papers, Handbook of Marketing Research, McGraw-Hill Book Company.