Compiler Error Guide

Looking for help learning to fish.
I’m building a couple of libraries for existing C code and am receiving a compiler error along the lines of “W-indow.obj: error LNK2019: unresolved external symbol…Error: execution of command failed with code: 2:…”. Looking for resources to get more familiar with the compiler and these arcane error messages. Any suggestions?

Commented out one line and it now compiles. Still would like to understand the internals of the compiler, just less time critical.

What did that commented line say?

It was a require statement within pointing to Google said error code 2 was related to file not found so I took a stab at commenting it out.