The poem's title tells readers that what follows all takes place "Near Naples," a coastal Italian city. The speaker then begins describing the world around him with simple observations that reveal the loveliness of the day at hand. He begins:
The Sun is warm, the sky is clear,
The waves are dancing fast and bright,
Note how the parallelism (bolded above) and asyndeton (or lack of conjunctions) immediately make the speaker's observations feel quick and straightforward. The metaphor of dancing waves, meanwhile, imbues the scene with liveliness and joy.
The next few lines are filled with more colorful imagery as the speaker describes "[b]lue isles," snow-capped mountains, and the "purple" light of midday. The speaker's use of personification also creates the sense that nature is truly alive all around him. The little islands and "mountains" aren't just tinted "purple"—they're "wear[ing]" the day's vibrant colors like clothes; the speaker calls the moist sea air the earth's own "breath," which is "light" as it surrounds flower buds that have yet to bloom. That those buds are "unexpanded" further suggests their unrealized potential; it's an image of hope and anticipation. And the sibilance of this passage (as in "dancing fast," "its unexpanded buds") subtly evokes the spray of the sea and the gentle hush of those dancing waves.
The poem's title doesn't just tell readers where things take place; it also tells readers that the speaker is feeling dejected, deeply sad, and alone. As such, while the speaker quickly, tenderly catalogs the beauty around him, readers might get the sense that he's trying to distract himself from his own pain and suffering.
This opening stanza also establishes the poem's meter: all these lines are in iambic tetrameter. An iamb is a poetic unit with an unstressed-stressed syllable pattern, and tetrameter means there are four iambs per line (for a total of eight syllables). Here's that meter in action in lines 1 and 2:
The Sun | is warm, | the sky | is clear,
The waves | are danc- | ing fast | and bright,
The steady iambic rhythm evokes the calm serenity of the day at hand.