Lines 1-4 establish the poem's main characters and initial setting. The poem's heroes are the pair mentioned in the title—"The Owl and the Pussy-Cat"—and they take a delightful trip to "sea" together. By the end of the stanza, it's clear that they're a couple, and they're madly in love.
In these opening lines, the atmosphere is already charming and romantic. The couple's boat is "beautiful," their food is sweet ("honey"), and their money is "plent[iful]." In fact, their money is "Wrapped up" in even more money! A "five-pound note" (similar to a U.S. five-dollar bill) would have had a lot of purchasing power back in 1871, when the poem was published. Basically, the Owl and the Pussy-Cat have everything they need for a happy, comfortable journey.
Of course, none of these details would make sense in the real world. Cats and owls don't fall for each other, don't sail in boats, don't typically eat honey, and don't spend money! The poem places readers firmly in the world of make-believe and "nonsense"—the term often used to describe Edward Lear's writing. Taken on its own terms, however, that world is playful and inviting.
Here and throughout, the poem uses a bouncy accentual meter. This means that its pattern is based on the number of stresses per line, but not the number of syllables or the placement of stresses. Note, too, that first eight lines of each stanza alternate between longer and shorter lines, making them resemble ballad stanzas. Generally, they also alternate between four stresses and three stresses apiece Listen to lines 1-2, for example:
The Owl and the Pussy-cat went to sea
In a beautiful pea-green boat,
(Some readers might argue that there's a stress on "green" there, but it's subtle.) There's also a boatload of rhyme, including internal rhyme ("honey"/"money"). These features give it a sing-song, nursery-rhyme quality that's ideal for a children's poem. (Lear originally wrote "The Owl and the Pussy-Cat" for a friend's three-year-old daughter, and it's remained a classic of children's literature for over 150 years.)