The very first lines of the poem give us a description: "The grey sea and the long black land; / And the yellow half-moon large and low." Fair enough, but it's not really clear what this description is doing because it's just sort of there. After about five lines, it becomes clear the speaker is on his way somewhere, and this is part of the setting. As the poem continues, the speaker gives us a list of more things; if it weren't for the title, we might be a little puzzled, but because of the title we presume the speaker is on his way to a meeting.
Either way, the poem is a bit confusing at first, and this is partly because of the unique, first-person point of view. In many ways the poem sounds like a monologue in somebody's head, and for that reason it can be hard at first to determine just what is happening. This is one of the hallmarks of Browning's mature poetry.