When you are trying to identify primary sources, think first-hand, contemporary, direct evidence or data, original records, artwork, writing, or research.
Hint: if someone is providing any kind of interpretation, summary, criticism, analysis, definition, or compilation of originals, you are probably straying into secondary or tertiary source territory!
Primary Sources: documents, audiovisual materials, objects or data sets created during the time under study. The viewpoint is from the inside.
Examples: Peer-reviewed articles/studies, transcripts, podcasts, musical scores, works of art and literature, interviews, artifacts, autobiographies/diaries, fossils, conference proceedings, specimens, eyewitness accounts, market surveys, data sets, photographs, government documents, websites, polls, television programs, tweets/posts/emails/texts.