Primary sources are the historical documents used by historians as evidence. Examples of primary sources include diaries, personal journals, government records, court records, property records, newspaper articles, military reports, military rosters, and many other things.
In contrast, a secondary source is the typical history book which may discuss a person, event or other historical topic. A good secondary source uses primary sources as evidence.
The key to determining whether an item may be considered to be a primary source is to ask how soon after the event was the information recorded. This can be a problem with an autobiography, memoir, reminiscence, etc. if the author is working several years with only the memory of what happened. Your history professor will disallow most or all of these as primary sources. However, the rule of thumb should always be: if you're not sure whether something is an acceptable primary source, ask your professor.
The ASU Library acknowledges the twenty-three Native Nations that have inhabited this land for centuries. Arizona State University's four campuses are located in the Salt River Valley on ancestral territories of Indigenous peoples, including the Akimel O’odham (Pima) and Pee Posh (Maricopa) Indian Communities, whose care and keeping of these lands allows us to be here today. ASU Library acknowledges the sovereignty of these nations and seeks to foster an environment of success and possibility for Native American students and patrons. We are advocates for the incorporation of Indigenous knowledge systems and research methodologies within contemporary library practice. ASU Library welcomes members of the Akimel O’odham and Pee Posh, and all Native nations to the Library.