Here are a few examples of some primary, secondary and tertiary sources. These sources may vary depending on the subject.
Primary sources are original materials.
They are from the time period involved and have not been filtered through interpretation, from the time period involved. Patents Photographs Proceedings of Meetings, Conferences and Symposia. Secondary sources are accounts written after the fact with the benefit of hindsight. They are interpretations and evaluations of primary sources. Secondary sources are not evidence, but rather commentary on and discussion of evidence.