Beginner's guide

Best guide around is The Fantastic Manual written by VeloCiryx

Not a guide, but worth reading are Soren Johnson's developer notes on Old World game design.

New player guide by Voqar: https://voqar.github.io/index.html

There is a set of guides linked on the subreddit: https://www.reddit.com/r/OldWorldGame/comments/gh6kfg/list_of_most_guides_of_the_game/

Donblas also wrote up a early game technology guide: Donblas' Early Technology Guide

Questions a player familiar with the Civilization Franchise might face: Questions a civ player might have.