Damage is the base of the spell or weapon plus the (tier dies times your tier level.)
Level 1 = base item damage + 1d4
Level 2 = base item damage + 2d6
Level 3 = base item damage + 3d8
Level 4 = base item damage + 4d10
Level 5 = base item damage + 5d12
The damage type for tier damage is the same as the largest base item damage.
The tier dies amounts pass through from the “roll to hit”. A second roll for damage is not required.