tell me its answer
It reflects the rather bleak, minimalist imagery.
There's the speaker, the man, under a tree. It's probably winter, there's snow on the tree, an evergreen pine called a hemlock, and a crow has happened to send some snow dust down on the man.
Whether it falls on to his head or down his neck is unknown because it's not really relevant to the poem. What is important is the way that crow makes it happen, but once again, the reader is left to imagine the bird's specific action