Well, what is your character class called? I just blindly assumed your character class was AFirstPersonCharacter. Just replace those AFirstPersonCharacter with the name of your character class name (which you probably can find in VisualStudio by looking into Solution Explorer or alternatively from Content Browser in UE Editor)
For example, if you can find MyProjectNameCharacter.h from VS Solution Explorer or if there is actor called MyProjectNameCharacter under “C++ Classes” in Content Browser, you get the name in code by simply prefixing that with an “A”, thus in this example that would make your character class name in code AMyProjectNameCharacter
Most of those ‘nodes’ exist as member functions and properties of the actor. For example, in answer above, you could access them with OtherActor->SetActorHiddenInGame(...)
A full list of AActor members can be found here, and from there it shouldn’t be too hard to navigate to other classes as well. Also, remember that UE4 documentation and google (or whatever is your preferred search engine) are your best friends
Well yeah, UE4 documentation can be quite quirky and limited when it comes to certain things. But in most cases for me at least API Reference and documentation (and of course google) have been enough to come up with solutions, even that it might have taken a hour or two of searching and testing things.