This is a poem about stroll through the streets of Manhattan on a beautiful, breezy March day. The poem starts with the speaker telling us that he's "ambling along 44th Street" in New York. (That's midtown, Manhattan, in case you haven't been lately.) And he's got his earphones on. He's listening to Sonny Rollins, a jazz saxophonist. What could be better than strolling around New York on a spring day with jazz tunes pumping in our ears?
According to this speaker, nothing is better. The rest of the poem is about just how awesome he feels walking around the city while listening to jazz—to the great tunes not only of Rollins, but of Tommy Potter, Arthur Taylor, and Thelonious Monk (if you don't know who these people are, you can just check out the "Shout Outs" section below to find out more about them). The speaker describes how close the music makes him feel to these guys. In fact, he feels so close to these musicians, it's as if they're walking right there next to him on the pavement, with their instruments and all.
Listening to these jazz musicians do their thing, the speaker feels like he's the "center of the universe" and the "hub of the cosmos" as he strolls around. The music kind of makes him feel like a superhero. And what does he hope to accomplish with his newly-acquired superhero identity? He's hoping to make it all the way downtown. So the poem ends on funny note: the speaker makes these grand claims about how the music makes him feel like the coolest, most awesome, most important person on the planet, and yet, his ambitions are pretty simple. All he's planning to do, as the coolest, most awesome, most important person on the planet is, well, to travel downtown—Superman, he is not.