Cite your sources: give credit, and leave a trail
You'll use Chicago Style for this class. Start here: Chicago-Style Citation Quick Guide.
See also:
Chicago Manual of Style Online (Cornell Library licensed resource)
Chicago Manual of Style, 16th edition (2010): Olin Library Reference Z253 .U69 2010 Shelved at the Reference Desk.
Citation Management (Cornell Library) General advice, and links to other style guides and citation management software.