Ranchera refers to a traditional genre of Mexican music, often associated with rural themes and passionate emotions. It's a culturally specific word that adds a unique flavor to the lyrics.
In the song, Carlos Vives sings about his love's "risa la ranchera" (ranchera laugh) while she's making margaritas. This imagery evokes a lively, joyful, and perhaps slightly dramatic personality, connecting her laughter to the expressive nature of ranchera music. It's an interesting way to describe someone's character through a musical genre.
Carlos Vives sings to a lover who has left, and the sofa in his living room becomes the whole wreckage of the relationship. He can't stop replaying her face — "Extraño tu sonrisa y tu piel de Mona Lisa" ["I miss your smile and your Mona Lisa skin"] — and the ordinary nights they spent together studying and dancing on that same couch. When she leaves, the objects around him keep grieving with him: "Como pesa que viene esta cruz, de no verte despertar en nuestro cuarto" ["How heavy this cross is, not seeing you wake up in our room"].
He doesn't try to move on. He leaves the door open, betting she'll walk back through it: "Cuando quieras puedes regresar, ya mi casa no puede esperar de encontrarte nuevamente entre mis brazos" ["Whenever you want you can come back, my house can't wait to find you again in my arms"]. The sofa stays right where it was, still waiting for two people to sit on it again.