Calaf (Domingo) having just been reunited with his father and his faithful servant Lui (Mitchelel), tells them he is going to try and win Turandot by answering her three riddles. It is certain death because no one has succeeded. Lui in desperation begs him to come with them and leave the city. Calaf replies in his aria "Non piangere Lui" (don't cry, Lui) which leads into the end of the act sextet with everyone trying to stop him.
The beauty of the music is that you can have several voices at one time "saying" different things; in a play that would never work. Everything would be jibberish. Enjoy!