Either A) understand the WriteProcessMemory API call defined via the windows.h header file, or B) Understand C++ pointers(Which you should at least if you're going to start simple hacking), and how a DLL works, along with how to create'em. If you do one of either of these you will know how to create simple hacks, provided that you know how the computer manages its memory, and you understand how to work with tools such as Cheat Engine.