I noticed that many amiga games, some people add an intro/trainer at the
start. For ex. lets you add infinite life, time, etc.
How can I learn to do this ?
what program to use, what to read, how to learn ?
1. Learn 68k assembler.
2. Learn to use ReSource.
3. Learn to locate the positions in the game code that decrease energy, lifes, or for example give weapons, or check if the player has collided with the enemy.
4. Learn to modify these locations in a way that the game logic changes. For example remove the instructions that decrease energy or lifes or detect the collisions. Call routine that gives all weapons. Usually this involves hooking the keyboard handler routine and checking if certain keys are pressed. If yes, patch the game code accordingly.
I would say it takes several years to learn just this. Oh btw, hex editor is totally useless here.
Note that I didn't even cover the intro coding. In most cases different people coded the intros and did the training, at least later on. They didn't use any demomaker.