I can recommend the tutorial guides too. They cost money, but you really got a lot of pages, and its well written. The first guide delve into the basics of coding. The second is more advanced stuff like 3D physics.
Start out with some stupidly simple game idea. You don't want to spend 200 hours coding, only to have to start over because it ended up an untangle mess. Far better to quickly finish a game, recognize your screw-ups, and do better next time.
AGK comes with a few games included. Try opening them and play around, see if any of it make sense. You can hold your mouse cursor over a code bit and press F1 to get help.
A general principle is to keep main file ultra short, a single screen length or so. Use it as the skeleton, the basic framework. Then place all the bits of code in functions in separate files.
Still, when I just try stuff out I just throws everything in the main file.
If you ask for help, remember to include your code.