Primary means written at or near the time of the historical event.
Secondary means written many years later, probably by a scholar researching the historical event.
Books are organized in the library by the Library of Congress Classification System. LC Subject Headings are assigned to every book. They will help you locate more relevant books on your topic.
You can find other videos on requesting materials from other libraries, accessing your My Library account, requesting group study rooms, and more at the Atkins Library YouTube Channel.