OOP Minecraft client

Hey mpgh Members,
I have been having some trouble with my Client, I've been trying to make the hacks such as Fly, FullBright, ect.
I don't understand how to do it. I've looked at some tutorials they just use someones source code and tell you to do it like that. Like no one really explians and uses there own code that they made for the tutorial. Back to the point I need help making a hack in OOP if anyone could explain how it's done and break it down for me that would be great!

This video does a decent job explaining how OO works in java.