"Meeting at Night" makes frequent use of alliteration and consonance. Generally, this is part of an overall strategy to build a sense of atmosphere and anticipation throughout the poem.
The first obvious example of alliteration is in line 1. In this line, the lolling /l/ of "long" and "land"—which also chime with the /l/ in "black"—create the sense of a huge, imposing landscape. The "volume" of the sound—the degree to which it imposes itself on the line—emphasizes the way in which the surrounding geography imposes itself on the speaker's experience while journeying to this meeting; in other words, the speaker can't avoid trekking through this landscape, and the insistent /l/ sound is a sonic reminder of that fact.
In the following line, the yellow moon is described as "large and low." The alliterative /l/ sound picks up on the /l/ sound found elsewhere in this line (i.e., in "yellow") and the first line. As with the previous example, the alliteration helps to create the poem's mysterious nocturnal atmosphere. The line is once again dominated by the /l/ sound, which has already been linked with the imposing landscape.
The very same sounds repeat again in the third line (also combining via consonance with "startled"). Here, "little waves ... leap." This alliteration is more about creating a sense of small and sudden movement, with the /l/ sounds "leaping" between the different stages of the line.
Later, line 5's alliterative /p/ suggests physical effort, the plosive sound causing the reader's mouth to exhale almost as if from exhaustion. It also suggests doggedness and determination as the speaker is "pushing" the "prow" (part of a boat) to shore.
The following line uses alliterative /s/ sounds—also known as sibilance—to try to replicate the sound of the thing that it's describing. The speaker is pushing their boat through "slushy sand," making a squelchy wet sound mimicked by the sibilance.
Yet another example of meaningful alliteration occurs when, in line 8, "fields" is linked with "farm." Apart from linking two nouns that are both related to agriculture, the alliteration here also creates the sense that the speaker is passing through separate stages of the journey. That is, the two /f/ sounds read like markers along the route to this meeting.