When you assist another player who's rolling, describe what your character does to help. Take 1 stress and give them +1d to their roll. You might also suffer any consequences that occur because of the roll, depending on the circumstances. Only one character may assist a given roll. If you really want to help and someone else is already assisting, consider performing a setup maneuver instead.

A character may assist a group action, but only if they aren't taking part in it directly. You decide which character in the group action gets the bonus die.