Your professor may require you to find scholarly sources popular sources, secondary sources or primary sources on your topic. Here's a very basic guide if you need more details:
Primary Sources: Primary sources are the raw stuff of history. Examples of primary sources:
Some Primary Sources are also known as popular sources.
Secondary or Scholarly Sources:
These are the peer reviewed articles and scholarly books that historians write after they have worked with the primary sources -- and consulted other secondary articles or books.
Historiography: Historiography is the study of how historians have interpreted historical events throughout time. The student of the historiography of South Africa, for example, might want to compare how historians wrote about the country during the Colonial and Apartheid eras with how historians have written about it during the last twenty years. One way of doing this comparative interpretation, is by looking for bibliographies on a subject or using the keyword "historiography" combined with keywords from the subject of your research