Will multi threading provide any performance boost?

Question

I am new to programming in general so please keep that in mind when you answer my question.

I have a program that takes a large 3D array (1 billion elements) and sums up

Answer 1

It's impossible to tell, in general, because you did not specify how fast your CPU and RAM are. Good chances are that it will improve things, because I can't imagine how even 4 threads summing in parallel would saturate RAM enough that it would become a bottleneck (and not the CPU).