Primary Sources are original sources: they were created by someone who participated in or observed an event. They include diaries, letters, newspapers, government documents, photographs, and other manuscripts.
We have many print collections of Presidential Papers in Gorgas Library. Just go to Scout or The Classic Catalog and do an author search (you'll need to use the drop-down menu by the search bar to change to author) for the president you're looking for (for example: "Reagan, Ronald"). This is a good way to find memoirs also!