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.
Google Scholar can be a good search engine for interdisciplinary research but there is no way of limiting your search results to "peer-reviewed" sources. You can search in UlrichsWeb by periodical title to ensure that the sources you plan to use for your research are scholarly, peer-reviewed.
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.