What do these metaphors mean in the poem? 1) The wind was a torrent of darkness 2) The moon was a ghostly galleon 3) The road was a ribbon of moonlight

"The wind was a torrent of darkness." In the first line of the poem Noyes is setting the scene for the action that follows. He's trying to create an appropriately dark and sinister atmosphere for the highwayman's imminent arrival. The first line of the poem simply means that it was very dark and windy on that fateful night when the highwayman came riding up to the old inn-door.
"The moon was a ghostly galleon." A galleon is a large ship, the kind you see in countless pirate movies. On that dark, stormy night in which the highwayman rides up to the inn, the moon has a strange, ghostly kind of appearance as it gleams among the storm clouds. The poet wants us to picture the moon as resembling a haunted ghost ship out at sea, tossed about by the crashing waves in the middle of a violent thunderstorm. As with the first line of the poem, this is all about establishing an appropriate atmosphere for the action that follows.
"The road was a ribbon of moonlight over the purple moor." It's already been established that the moon is shining. And as the moon casts its light upon the earth, the road on which the highwayman rides his horse appears to have been transformed into a long ribbon of moonlight. In the stormy darkness, lit only by the moonlight, the moor has taken on a kind of purple color. Like all other features of the landscape, it's been completely transformed by the darkness and the moonlight. It's as if a whole new world has suddenly sprung up out of nowhere.
https://www.poetryfoundation.org/poems/43187/the-highwayman