Casting: the caster spends Will to roll that many dice, plus any free Will dice (from a staff, for example). The power is cast if the highest die equals or beats the casting value.
Channelled: costs 1 Will and 1 Might, and the casting roll counts as a 6, so the power is always cast. The target then has to match a 6 to resist it.
Resisting: if the power is cast, the target may spend Will to roll that many dice, plus any free dice. It's resisted if any die equals or beats the caster's highest die. Will is only spent on resisting when the power is actually cast.
Might on casting: if the highest casting die falls short, the caster spends just enough Might to raise it to the casting value. Might on resisting: if the highest resisting die falls short, the target spends just enough Might to match the casting score.