If you wanted to research the problems of the elderly in our community, you could choose to interview residents of a local convalescent hospital. This would be a primary source. If you wanted to research the field worker experiences during the Delano Grape Boycott, you could find interviews or diaries of agriculture workers or union leaders and members during that period. These would also be primary sources. Diaries, letters, interviews, autobiographies are generally all good sources of primary evidence.
Primary sources are also the data that other researchers have compiled and published.
Secondary sources are one step removed from the original, and usually involve examination, observation, review, analysis or commentary of the primary source of information. Examples of secondary sources are critical reviews, biographies, journal articles, encyclopedias, and handbooks. Secondary sources provide the opportunity for analysis, evaluation, a look at the big picture, or the event in context with other events. They also may be biased, taken out of context, or misinterpreted. To research the problems of the elderly, you might read reports from state agencies, or local newspaper articles.