You may come across the terms primary sources, secondary sources, and tertiary sources.
Primary sources are original works or research before it has been commented on, analyzed, or interpreted. Examples include diaries, letters, and photographs.
Secondary sources provide commentary or analysis on primary sources. Examples include journal articles and books.
Tertiary sources consist of information which is a distillation and collection of primary and secondary sources. Examples include bibliographies, dictionaries, encyclopedias, and directories.
Where you find primary sources depends a lot on your discipline or field of study.
For literature students, the primary source is usually the text (novel, story, poem) you're studying. For art students, the primary source would be the artwork.
Historians often look for primary sources in archives, and more and more this archival content is being digitized and made available on the Internet.
In the sciences, the research that scientists are doing would be considered the primary source.
Check out the History Subject Guide for links to various digital collections of primary sources.
The following sub-headings can be added to subject headings when searching for primary sources: