An example of secondary source is

A secondary source is one that interprets or analyses primary sources. C.A. Bayly's 'An Illustrated History of Modern India' is a historian's interpretive work based on primary sources, making it a secondary source. James Mill's 'A History of British India' (1817) is a primary source from the colonial period itself. The Constitution of India is a primary source (legal document). A painting by Abanindranath Tagore is a primary source (created during the period and reflects contemporary viewpoint).