In general? At it's basis a mole sauce is a chile sauce and along with different roasted chilies, it can contain numerous components. It's a notoriously labor intensive sauce to make which is why I've never made one from scratch, but used pastes to start and then add what I feel like. Perhaps the most well known version incorporates chocolate in it which gives the sauce a sweetness that is balanced by the bitter, earthy and savory aspects of the sauce. And of course the chilies bring some heat to the equation. Not all mole sauces have chocolate in them, though. But they all start with chilies.