im new and just for the sake of talk what would someone need to build a hack for a online pc game. is it very difficult what things would i need to know before hand etc.
What you will need to know will many be determined by what game your trying to hack and how complex it is. And by hack im making the assumption that you mean make a bot or trainer of some kind. For pretty much any main stream game you will need a pretty solid understanding of programming in general not to mention you will also need knowledge of bypassing systems like gamegaurd if the game uses one and agin most main stream games do.
If your interested in learning look into tools like cheat engine and there are plenty of tutorials on how to get started
If you're looking to make game hacks as a hobby, you'll want to start out with java. Modding and hacking games made in java is relatively easy, as java is a weak game programming language. Games such as minecraft offer open modding and there are many tutorials on their website teaching you how to mod. Hacking is a new story, a hacker needs to know the language very well to know how to wiggle through the games security and code an undetectable hack. To answer your question, it is very difficult.