Game hacking is something that hackers do to cheat in games, the most of the game hacks are written in C++ language, but there are also hacks in C# and Visual basic(For some web based games, like flash) Or singleplayer game trainers.
There are many ways to hack a game. Mostly used is the memory editing, with your own software you could edit your own RAM memory while the computer is running. So let's say that you are playing some kind of a FPS game which is a multyplayer game, and it has on hack protection, Your program finds a memory code for example.. HealthPoints , the code is something like 0x1243242 that <- , and that address has its own value. For example the HP is 100, let's say that you get hit from someone, and your HP is now 50, and you want to hack the hp to be invincible? You tell your program to overwrite this address every 1 millisecond to 100, so if someone shoots you, your hp will always be FULL .