Three short lines, and almost nothing happens. A speaker sits and watches steam drift up from the pavement. That's the whole scene, and the poem's quiet is the point.
The poem doesn't say why the pavement is steaming, but the image suggests heat meeting moisture, perhaps sun after rain, though that's our guess, not something the words confirm. What matters more is the speaker's stillness. "Sitting here" sets them in the present moment, with nowhere to go and nothing to do except look. The word "watching" makes the act feel patient and unhurried.
The mood is calm, a little dreamy, and maybe a touch lonely, since no one else appears. There's no stated emotion, so the feeling is left for you to supply. Some readers may find peace in it; others may sense idleness or a mind drifting. The brevity mirrors the experience: a small, ordinary sight that holds attention just because someone stopped long enough to notice it.