The game can be about anything, right? No limits? And about the rule "Anyone who makes games can participate", does that mean that you would have had to previously made a game? Or is it meaning to say that anyone can join? Okok last question I promise, any program is fine, right? Like you can use the worst of the worst? (a.k.a twine, not to bash people who do use that)

Yes, it can be about anything. (Unless it's something like hate speech against a race, or something that can't be in itch.io)

It is quite okay if that's going to be your first game.

Any program/tool can be used.