Primary resources are sources created by people who were actual eye witnesses of or participated in an event and then wrote or recorded the information about it soon after it took place.
Primary resources can take the form of various types of materials such as pictures, photographs, poems, court records, interviews, diaries, notes, oral histories, memoirs, posters, etc.
For example, an article written in a newspaper during World War II by an eye witness of the fighting is primary material as well as a letter written by a soldier to his family during World War II.
However, an article written analyzing the results of the battles fought during the World War II is secondary material. Usually, a work that is analyzing or interpreting the events that occurred during a historical event or period is considered a secondary resource.
Primary resources vary by discipline. It is best to check with your professor to see what he or she considers a primary resource.