I'm making a simple game in c++, using Visual Studio.

I have a bunch of functions for various things on a file called "engine.h" and then in "main.cpp" I have actual game stuff (levels and map)

I've been trying to put these into classes and then separate the classes into files and include the header files (I think this is called definition and implementation or something like that.)

But every time I try to do this, I get a ton of LINKER errors and have no choice to revert to the 1 header file system. The Linker errors are mostly "LNK2005" and "LNK2001"

Does anyone know how to do this properly? Other than organization, are there any other adverse affects of having all my functions on one header file?

Thanks!