Primary sources are original, uninterpreted information.
Unedited, firsthand access to words, images, or objects created by persons directly involved in an activity or event or speaking directly for a group. This is information before it has been analyzed, interpreted, commented upon, spun, or repackaged. Depending upon the context, these may include paintings, interviews, works of fiction, research reports, sales receipts, speeches, letters, e-mails, and others.
Think of physical evidence or eyewitness testimony in a court trial.
Secondary sources interpret, analyze or summarize.
Commentary upon, or analysis of, events, ideas, or primary sources. Because they are often written significantly after events by parties not directly involved but who have special expertise, they may provide historical context or critical perspectives.
Think of a lawyer's final summation or jury discussion in a court trial.