How to create and implement the << operator for my program, specific to a Value class, and to be used for printing

I've been searching online for days on how to create a << operator for my assignment. Whatever I found online doesn't seem to work for the assignment I have. I would really appreciate help and guidance on as to where to create the << operator for my program. One of the directions by my professor is "implement operator<< for Value (for use by print)". I'm posting the link to the same question on cplusplus.com, which include my ParseNode.h and ParseNode.cpp file. For some reason I couldn't get the code to appear properly here.

Link: http://ift.tt/2oUmfwN