Use a tiny RPG system[1] with a tiny environment ready-made environment[2].
Familiarise yourself with how others[3] run the same environment, then make it your own! You got this.
[1]: System (free). https://yochaigal.itch.io/cairn
[2]: Environment (free). https://v6p9d9t4.ssl.hwcdn.net/html/6466170/BotEk/index.html
[3]: An actual play of the environment (free). https://www.youtube.com/watch?v=e3N4pqHIEwQ