"The Snow Man" uses two types of imagery to bring the winter scene to life on the page.
In the first two stanzas, the speaker describes the winter landscape:
One must have a mind of winter
To regard the frost and the boughs
Of the pine-trees crusted with snow;
And have been cold a long time
To behold the junipers shagged with ice,
The spruces rough in the distant glitter
Of the January sun; [...]
These lines conjure up a wilderness of frozen evergreens: "crusted" and "shagged," they're dramatically engulfed in ice. The imagery paints a severe-but-beautiful picture that subtly challenges the reader not to automatically personify this scene as miserable. Note, too, how delicate sound work makes the images all the more evocative (e.g. the light /t/ consonance that evokes the "distant glitter" of sunlight on ice).
From line 8, the poem switches to auditory (sound-based) imagery. The speaker describes:
the sound of the wind,
In the sound of a few leaves,
Here, the speaker presents the sound of the wind in the plainest possible terms—it's just the "sound of the wind," audible only because of the movement of "a few leaves," creating the only "sound of the land." This shift away from the vivid language of the first two stanzas again challenges the reader, because it's hard to read these stark lines without imagining "misery in the sound of the wind."
In different ways, both types of imagery challenge the reader not to make judgements about this winter world, instead simply seeing and hearing it alongside the speaker. The true "snow man," the speaker suggests, doesn't think of the scene as beautiful or harsh—or as anything at all.