The type of assignment will also determine what type of material to use. Decide whether it is appropriate to use an encyclopedia, books, journal articles, or all of these. Some types of resources are more appropriate for specialised purposes than others. To take one example, encyclopedia articles are usually not included in an annotated bibliography. The distinction between these different sorts of information is extremely important.
Primary sources contain original information.
They can include original manuscripts, contemporary records, reports, photographs, documents used by an author in writing a book, patents, maps, statistical tables, diaries, letters, original artworks, journal articles reporting original research, etc. Primary sources are particularly useful in that they contain details that are often ignored or left out by the people who write the next sort of resource. Secondary resources occur when primary sources are compiled, modified or rearranged to produce material for a specified purpose or audience. Examples include biographies, reviews, histories, collections of abstracts, bibliographies, journal indexes, commentaries, analyses, criticisms of literature or art. Consulting secondary sources can save you lots of time, and you get the benefit of the author's knowledge and expertise.