Though it makes some tweaks, for the most part Baldur's Gate 3 is very faithful to the rules of Dungeons & Dragons 5th edition—which means a grounding in tabletop role-playing makes it much easier to get to grips with its complicated RPG systems. That's a little daunting if you've never rolled a d20 in your life, but never fear: my quick and simple cheat sheet will get you up to speed on what all the most common D&D terms mean, and how they work in Baldur's Gate 3.
