The Dungeon Master physically rolls all the dice. He does not post the values, only the results of the actions
It goes like this:
FiberWire: I slash the goblin with my longsword!
(DM rolls dice)
DM: Your blow lands squarely on the goblin's head. Its knees buckle and it collapses, motionless. Angered by their comrade's death, two more goblins charge screaming towards you!