The speaker finds himself among a group of tar-workers and sets out to teach himself what tar actually is. His answer is oddly homely: a "great batter," something you might stir and cook, boiled until it is thick and simple, "like a fool." That last phrase could describe the tar or the speaker himself, and the poem seems happy to leave it unclear.
The second half widens the scene. The night "took / a few turns in my coat," as if darkness were wandering around inside his clothing, or as if he had been pacing through it for hours. The closing line, "I found the pageant strange," steps back from everything. The tar-men become a kind of procession or show, and he watches as an outsider.
The mood is dreamlike and a little uneasy. Nothing is explained, and the speaker sounds calm, curious and slightly out of place, taking in an unfamiliar world one odd image at a time.