Historians often apply the Chicago Manual of Style (CMOS) when citing sources. Beneficially, the library provides online access to the complete CMOS ebook. Zotero can also generate CMOS citations.
The Chicago Manual of Style by University of Chicago Press Editorial StaffOnline access to the complete and up-to-date contents of the 17th edition (2017). Leyburn Library has a printed copy. If you are looking for help with documentation (footnotes, in-text citations, bibliographies), you probably want Chapter 14 and/or Chapter 15. Chicago Style is a good general-purpose style and is often used in history and other fields within the humanities.