The poem opens on a young man who has been injured in war. He has now returned from the war, but his life has changed irrevocably. His name is never specified, nor is the town where he's from. This lack of specificity lends the poem a sense of universality, suggesting that the man's story is as common as it is tragic.
Sitting in a "wheeled chair," the young man "wait[s] for dark." The fact that he's in a "wheeled chair" suggests that he must be pushed around by the staff who work in the hospital, especially since he has lost the lower halves of his arms—as made evident by the fact that his hospital-issued clothing is both "legless" and "sewn short at elbow." The implication here is that he can't operate his wheelchair because he doesn't have any forearms, though this isn't necessarily an accurate reflection of what is and isn't possible for wheelchair users. Nonetheless, the young man's immobility will, as the poem goes on, form an important sense of juxtaposition with the energetic activity of his pre-war youth.
Alliteration between "wheeled" and "waiting" links these two words together, highlighting that all the man can do is sit around and wait for others. Instead of doing things himself, he has to wait for things to happen to him. The suggestion that he's "waiting for dark" could mean he longs for the comfort of sleep, but it also might refer to the eternal rest of death. This seems particularly likely, given that the rest of the poem implies he doesn't feel life is worth living anymore.
His "ghastly" gray suit almost portrays him as one of the living dead—like a zombie of sorts—and his shivering underlines this lack of life or vitality. Gray, after all, is a very drab and lifeless color, indicating a certain absence of warmth. This description of the young man's clothing also suggests that he's a shadow or ghost of his former self; the alliteration between "ghastly" and "grey" emphasizes that the man himself sees his suit as terrible and ugly, perhaps hating that he has to wear something so depressing and lifeless.
In line 3, the poem's pacing is blunt and unsparing. The man is "legless," the poem states, and this word is isolated (or severed) by the caesura that follows it:
Legless, || sewn short at elbow. [...]
This calls attention not just to the fact that he no longer has any legs, but also that his arms have been cut off at the elbow. The caesura after "elbow" spotlights the same thing, cutting the sentence short before the end of the line in the same way that the young man's limbs were cut short as a result of the war.