After logging in to JSTOR, enter your search terms and then use the Refine Results section on the left to view different types of primary source content.
The video "Find what you need quickly on JSTOR" goes over general searching tips when using JSTOR. This is for searching for any type of content on JSTOR, not only primary sources. It goes over how to login to JSTOR, searching, refining your results, browsing subject categories, and how to cite, save, and download.