thank you very much!! It's the quick start I was looking for.
I have an Assembler project which was a conversion of an Atari2600 game. After the birth of my son and the break of the project, I have no chance anymore to understand my very own Assembler code I think I stopped it when I was about to implement Enemy AI. Something which is no fun in low level ASM syntax and grown cryptic codebase. Because everything (sound, gfx, screens, pmgs, etc.) is finished I thought about reprogramming the game again - but this time using CC65. Now I have a good starting point.