A secondary source is one that was created after the event by someone who wasn't there. Examples include books, journals, magazines and websites. It isn't one that is secondary in importance!
For your paper you need to find scholarly sources. The slides below tell you the difference between a scholarly and non-scholarly source. If you're not sure, ask your teacher or a librarian.
How do you know if an article you find is scholarly? Look at the chart in this presentation to help you work it out. Make sure you are looking at an article NOT a book review (though you can look for the book if it sounds worthwhile). If you're still not sure, ask a librarian or your teacher.
Look at the SFPL Libguide for resources available through the San Francisco Public Library. You will need your card number and PIN to access them. SFPL has access to scholarly articles and eBooks.
The video below provides in-depth instruction on using Proquest to find academic articles and can be played as you search your own topic. The examples relate to the Mexico research paper you did in 9th grade, however the advice is excellent.