There are two main types of sources:
1) Primary Sources
Primary sources are the materials that contain direct evidence, first-hand testimony, or eyewitness accounts of topics or events under investigation. Subsequent interpretations or studies are based on these sources. Examples include anything from diaries, oral histories, memoirs, court records, correspondence and interviews to research results generated by experiments, surveys, etc.
Primary sources are immediate records of events, usually produced by witnesses or participants in the event. However, memoirs or interviews conducted years after an event are still considered primary source materials.
Visual materials, such as photos, original artwork, posters, and documentaries are also important primary sources, not only for the factual information they contain, but also for the personal insights they contain. Primary sources may also include sets of data, such as census statistics prior to interpretation.
2) Secondary Sources
Secondary sources offer an analysis of primary sources; they often attempt to describe or elucidate primary sources. Some secondary sources also use them to argue a position or persuade the reader to accept a certain opinion. Examples of secondary sources include dictionaries, encyclopedias, textbooks, and books and articles that interpret, analyze, or review research works.Secondary sources can be interpreted as primary sources when the artifactual characteristics of the item are of research value.
Good, solid research requires the use of both primary and secondary sources. Primary sources provide the raw data for your research, but you will also need encyclopedias, dictionaries, subject guides and other resources to gather background information on your topic, i.e. identifying people, places, dates, organizations, and themes central to your topic.
Secondary sources such as books, scholarly journals, and newspaper articles synthesize current research and help put your subject in context. They are also useful for helping you establish your argument based on the scholarly communication around your topic.
Use library catalogs, databases, printed reference sources, the web, and the assistance of your librarians to identify, locate, and use primary and secondary sources.
Also note that primary and secondary sources are not mutually exclusive. For example, a dictionary is a basic secondary source; but for someone studying the history of the dictionary, it becomes a primary resource. It is the way we use or interpret an item that determines whether it is a primary or secondary source.