The second act picks up where the first act ended. Romeo has left the Capulet household and is too full of his new passion to go home or to attend any other activity. Mercutio and Benvolio also leave the Capulet household and come looking for Romeo, but Romeo would rather be alone with his new feelings than with his friends; and, so, he hides from them.
Benvolio and, especially, Mercutio are both quite exhilarated from the night’s festivities: they probably have been drinking more than just a little as well. In a merry mood, Mercutio calls out after Romeo. The witty companion thinks that Romeo is still in love with Rosaline, and he wishes to tease him about his love. Mercutio jokes that calling upon Venus and Cupid will have a miraculous effect and produce Romeo as if by magic. Mercutio also makes an allusion to the ballad of King Cophetua and the beggar maid (at line 14). In this story a king falls in love with a poor woman and makes her his queen. The story was, perhaps, a prototype of the Cinderella fairy tale. Mercutio is negatively suggesting that the same powerful force that caused a great king to love a beggar is also responsible for causing Romeo to love Rosaline, whom, Mercutio thinks, is totally unsuitable for Romeo. Mercutio continues to make sexual jokes at Romeo’s expense and refers to the medlar tree (the fruit of which bears a slight resemblance to female sexual organs).
Romeo, however, wants nothing to do with Mercutio’s nonsense and comments (to himself) that Mercutio’s jokes about love are equivalent to a man jesting about a soldier’s wounds when that jesting man never received even a small wound himself (at line 43). Romeo is saying that Mercutio knows nothing about love since he has never been in love himself.