I think the title means that the narrator is stopping by unknown woods on a snowy night. Maybe he is delivering something.
tone and shifts
The narrator stops by unknown woods.He may know who owns it. He thinks his horse is confused to why they stopped. Its the darkest evening of the year. The horse is very confused.It is quiet and peaceful. he wants to stay but he has to keep going.
Alliteration: The only other sounds the sweep personification: The horse must think it queer