During Scene 4, what directions does Romeo have for Juliet and for the Nurse? What is about to happen at the end of Act II?

Romeo gives clear instructions to the Nurse to pass on to Juliet;

Bid her devise some means to come to shrift
This afternoon;
And there she shall at Friar Laurence’ cell
Be shriv'd and married.

Juliet has to come up with some way of getting to a confession ("shrift") that afternoon - and when she gets to her "confession", she will in fact be married.

The nurse gets a different set of instructions:

And stay, good nurse, behind the abbey wall.
Within this hour my man shall be with thee
And bring thee cords made like a tackled stair,
Which to the high topgallant of my joy
Must be my convoy in the secret night.
Farewell. Be trusty, and I'll quit thy pains.
Farewell. Commend me to thy mistress.

She is to wait behind the abbey wall, while the two are married. Romeo's servant will bring her a rope ladder ("cords made like a... stair"), which he will use to climb into Juliet's bedroom at night to consummate their marriage (i.e. have sex with her).

Of course - what is to happen at the very end of the act is that the wedding will take place: only hours before Romeo becomes a murderer by killing Tybalt.