Basic C++ Questions

Thanks for the help guys but so far I feel like I’m going in circles a little bit, just confusing myself.

I just want to bring it right down to basics quickly and ask if what I am doing wrong

Got a class called FPSTest with a function called FuncTest() that prints out some text to the screen with AddOnscreenDebugMessage.
I want to be able to execute that function from within my FPSCharacter class, simple right? Not for me!

I thought it would be as simple as writing something like (simplified)

FPSCharacter.cpp

Someone put me out of my misery please! Haha