Rain is the whole subject here, and the speaker isn't describing a storm so much as savoring it. The poem is built from three short, matching phrases: how rain smells in summer, how it looks on the pavement, how it feels on skin. Each one uses a different sense, so by the end you've smelled it, seen it, and touched it without a single full sentence being spelled out.
The title, "Bliss," tells us how the speaker feels. There's no complaint about getting wet and no worry about plans being ruined. Rain is simply a small, ordinary pleasure worth stopping for. The repeated "how" gives the lines a gentle, almost list-like rhythm, as if the speaker is counting favorite things and could keep going.
The closing ellipsis matters too. It leaves the last image hanging, like a moment you don't want to end. The mood is calm, fresh, and quietly happy, the feeling of standing outside and letting the rain do its thing.