It's not enough to #include the header. That only provides enough information for the compiler to verify the functions in the header are being called properly. In order to actually *use* the functions, you must compile the .cpp as well and link it with your code.

Either add the .cpp to your project, or compile it into a static library and link it with your project.

Unresolved external symbol means *exactly* what it says. There's an external symbol (something from the .h file) which the linker can't resolve, because it doesn't have access to the cpp file that defines it.