Please help me explain the dramatic irony of three passages from Romeo and Juliet. I don’t get it at all.

Answer:
Dramatic irony is when the reader or audience knows something the characters do not.
Explanation:
The other dramatic irony in Act II is that in Scene 1 and 4, Mercutio and Benvolio think Romeo is still pining over Rosaline, but the audience knows he is over her and has moved on to Juliet.