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 research reports, sales receipts, speeches, e-mails, original artwork, manuscripts, photos, diaries, personal letters, spoken stories/tales/interviews, diplomatic records, etc.
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. Examples are scholarly books, journals, magazines, criticism, interpretations, and so forth.
Think of a lawyer's final summation or jury discussion in a court trial.
Tertiary sources compile, index, or organize sources.
Sources which analyzed, compiled and digest secondary sources included mostly in abstracts, bibliographies, handbooks, encyclopedias, indexes, chronologies, etc.
Think of an index that lists all the cases heard by this court during the year.