Lines 1-5 establish the poem's setting, start to describe its action, and introduce the voice of the speaker.
From the start, the title frames the unnamed first-person speaker as "a Disappointed Man." The poem is supposed to comprise an entry in his "Journal" and possibly illustrate his general sense of disappointment. Rather than discussing his mood, however, the speaker tells an anecdote.
He reports that, while out and about for some unstated reason, he "discovered" a crew of workmen "driving a new pile / into the pier." That is, they were installing a new vertical support column on a dock, which seems to be a familiar local landmark for the speaker ("the pier"). Right away, the verb "discovered" is interesting: "saw" or "noticed" would be more expected in this context, but to the speaker, this ordinary scene constituted a discovery. The rest of the poem will show that he found it strangely absorbing and memorable.
The speaker describes the scene in lines full of alliteration:
I discovered these men driving a new pile
into the pier. There was all the paraphernalia
of chains, pulleys, cranes, ropes and, as I said,
a wooden pile, [...]
These plosive /d/ and /p/ sounds seem to convey the percussive noise of the construction site. Presumably, the workmen are maneuvering their heavy equipment, or "paraphernalia," as they prepare to install the "pile." When the speaker encounters the scene, the pile, which is "massive" and "wooden," is dangling from a "crane[]" on a "long wire hawser," or cable. Playful enjambment between stanzas (lines 4-5) makes this image seem to hang in the air for a moment, too:
[...] a wooden pile, a massive affair, swinging
over the water on a long wire hawser.
Enjambment creates similar effects throughout the poem, leaving words/phrases dangling over line breaks—and readers dangling in suspense—until the next line finishes the speaker's thought. (Another example is the enjambment in lines 1-2, which leaves the word "pile" itself hanging at the end of the first line.) In general, dangling, suspension, incompleteness, etc. are central to the poem's imagery, narrative, and themes. They seem to correspond with the speaker's persistent sense of "Disappoint[ment]."