Just to clarify, do you mean being a moderator for the speedrunning leaderboard, or like creating/using game mod(ification)s? Since we're in the Speedrunning forum I'm guessing you mean the former, but your wording is throwing me off.
For leaderboard moderation, that's not really something you just try out to see if you like it. Nobody really does it because they like it, they do it because someone has to do it. In any case, most games are generally not looking for new moderators at any given time, and the ones that are usually only want to bring on people that run the game and are actively involved in the community. So if none of the games you run and are actively involved with need new moderators, then you're out of luck, try again later.
For game modification, creating them is always a pretty involved process if you don't already know anything about how games work, so I don't think there's any "easy" way to get into that. Using existing ones is usually as simple as just finding one that you want to use and following the instructions.
