A Boon adds 1d6 to a roll. A Bane subtracts 1d6.
Count all applicable Boons and Banes, then cancel them one for one. After cancellation, a roll can have no more than two Boons or two Banes.
For example, three Boons and one Bane result in two Boons.
Rules and circumstances may grant Boons or Banes. The Game Master decides when the situation provides one. Different descriptions of the same advantage or disadvantage do not grant additional dice.