Most of the time, for print materials, the location refers to the exact page or pages where you found the information that you are using.
Example Alex Garton, Exploring cognitive development: The child as problem solver, (Malden, MA: Blackwell, 2005). 45-46
Online Materials
For a source obtained online, you will need the following.
date accessed ex: accessed November 23, 2017
One of the following three:
URL of the source where the resources was accessed
the database name where the resource was accessed
the DOI of the article
Examples
Print Materials
Alex Garton, Exploring cognitive development: The child as problem solver, (Malden, MA: Blackwell, 2005). 45-46
Online Materials
Daniel Keizman, Mark Ish-Shalom and Frank Konikoff, "The Clinical Significance of Bile Duct Sludge: Is it Different from Bile Duct Stones?" Surgical Endoscopy 21, no. 5 (April 2004): 769-773. doi:10.1007/s00464-006-9153-0