How to program multiple processor cores?

Question

I want to program some processor cores to perform a task in a way defined by me.
How to do that? How can i write a program to do so? can this work for me or not

BOOL SetProcessAffinityMask( HANDLE hProcess, DWORD_PTR dwProcessAffinityMask);

Am I required to do assembly language programming or something?
If yes, then how?

Does anyone have any suggestions?