The poem is a tiny, odd portrait of a street musician and the instrument he plays. The speaker describes it as "a fat foot with no bone," a strangely soft, lumpy image that suggests something clumsy, bulky, and a little comic. It might be an accordion or something like it, though the poem never says, so that's only a guess from the description.
What makes it interesting is that the instrument seems to talk. It tells the speaker to "fit myself for bed," as if the music is a tired, humdrum order to give up and go to sleep. Then it turns to "a beggar," which may be the busker himself, and tells him to "meddle / or make wit." That choice feels like a challenge: interfere pointlessly, or be clever and make something of your situation.
The mood is wry, slightly weary, and playful. There's humility in being a beggar, but also a stubborn wish to turn poverty into creativity. The short lines make the poem feel as quick and offhand as a passing tune.