Before you can run the .prg, you have to generate it. You can press F5 to build the game (.prg) and then F9 to run it, or you can press Ctrl+F5 which does both operations in sequence (of course, before, you've to configure the C64 Game Maker, see my introduction video for details). As for programs to generate games on the C64 directly, there are some, like the SEUCK (Shoot'Em-Up Construction Kit) to create vertical scrolling games without writing a single line of code (scrolling that I will support in a future version of my tool) and others like "Garry Kitchen's GameMaker" or "Arcade Game Construction Kit". However, using these tools on the C64 is not very practical in my opinion, the PC offers a much more advanced user interface and experience. But these are tastes!
Thanks. Ok you are going to add a vertical mode .
Yes, the original versions of these programs should not be obvious to use on the original C64. But it's true that I would have liked some kind of OS to be able to create things on the machine to be able to use it for something other than playing on it because I find the hardware very pleasant to use... that's what it is Apparently the Commodore 128 was more pleasant to use for coding games, it would have been good with current knowledge to create a sort of cartridge interface on the c64 for use in creation, images, video games (with c64 basic code editor), sprites, music...