Dungeons are designed in such a way that the mechanics are either obvious or that you'll figure them out really quickly, even if it takes 1 death to think: "oh, that's how it works". They often introduce mechanics to you one at a time, before putting them all together in sequence to test if you figured them all out. You don't need a guide, but having a mechanic explained that is less obvious and more deadly may save you from dying unnecesarily.

I choose to just go through a dungeon and not explain anything unless asked, so that they can do it blind if they wish. If they repeatedly mess up a crucial mechanic I briefly explain it after the fight so that they know for next time.