"Niña Bonita" is a love song that is also a song about writing a love song. She asked him for one, "que en ti me inspirara una canción linda" (that I'd write a pretty song inspired by you), and this is him delivering. He even admits his style has changed for her: he used to write happy stuff, "pero ahora romántico" (but now romantic).
The chorus is pure close-up detail. Who wouldn't be inspired, he asks, seeing "esos huequitos en tus mejillas" (those little dimples in your cheeks)? Huequitos literally means "little holes", and it is a sweet, very Colombian way to say dimples. The second verse gets more urgent: "La noche fue corta, no pudo ser larga" (The night was short, it couldn't be long), and he hopes whatever road she takes "te lleve conmigo pa' toda la vida" (takes you with me for the rest of my life). Note the pa', a squashed para you will hear everywhere in Caribbean Spanish. And yes, the "lararailara" bits are exactly what they look like: a hummable vallenato hook with no words to learn, so just sing along.