A primary source is original information. It could be:
A secondary source is an interpretation, analysis, commentary, riff, or basically anything about a primary source. Examples of secondary sources include:
Articles that come from scholarly journals are authoritative and are some of the most helpful sources that can help you support the argument that you are making. Scholarly books are also authoritative sources.
The library is the best place to find scholarly journals and books.
For most disciplines, peer-reviewed articles are the gold standard and help you to avoid most incompetence and misinformation. Watch this video to find out about the process of peer review.