This product is a prewritten adventure only, so you need an OSR / ODND ruleset to make a character and the mechanics to run it. There are countless rulesets at this point. You can get a lot of them free here on Itch if you search with the tag "OSR" and I'd recommend "rules-lite" to get one that is easy to start with. Castle Grief has one too called Kal-Arath that is designed for solo and group play. https://castlegrief.itch.io/kal-arath