The Nurse makes this comment about Paris after Lady Capulet has just informed Juliet that the young man wants her hand in marriage. The Nurse exclaims:
A man, young lady! lady, such a man
As all the world- why he's a man of wax.
Essentially the Nurse means that he is a very handsome man. In fact, the figure of speech he is so handsome that he does not look real. He must have been carved from wax. This is one of several humorous interjections the Nurse makes in the conversation between Juliet and her mother. This scene provides a bit of background: Juliet, who has yet to meet Romeo at this point, is expected to meet Paris at the Capulets' ball, and it is clear that Paris is a very worthy suitor.