Who is Juliet's messenger in Act II, Scene 4, and what are some of the issues she and Romeo discuss?

Juliet's nurse is her messenger in this scene, and Juliet has sent her to Romeo to find out what arrangements he has made with Friar Lawrence for their nuptials.  Before Romeo left Juliet's garden the night before, Juliet promised she would send a messenger to him early in the day.  Initially, Mercutio gives the nurse a hard time, insulting her and making inappropriate and lewd jokes towards her, and the Nurse becomes pretty angry with him.  After Benvolio and Mercutio leave to go to Lord Montague's house, the nurse and Romeo can speak in private. Romeo asks the nurse to offer his greetings to Juliet and to

Bid her devise

Some means to come to shrift this afternoon,

And there she shall at Friar Lawrence' cell

Be shrived and married (84-87).

Romeo wants Juliet to make up some reason to go and make confession today, and, when she arrives, Romeo will be there, prepared to marry her.  He's already made arrangements with the Friar to do so.