So, I've watched a tutorial and installed the needed files including "Simple trainer" but then what? If I try the Online mode the game crashes and in story mode, well, you have to follow the script of the story so how do I play and have fun being God and cause general mayhem like in this vid:
I tried that GTA V online thing couple years ago. If i remember right, you have to watch couple story videos where your character arrives to Los Santos and do couple little things for example meet somebody and do something what works as "tutorial" teaching you stuff what you can do. After that you are free to go fooling around.