The Shakespearean sonnet that is the prologue of Shakespeare's Romeo and Juliet provides a remarkable amount of information in just fourteen lines of iambic pentameter.
The first quatrain (the first four lines) of the sonnet introduces the characters in a general sense ("two households"), tells the audience that the two households have the same high social standing ("both alike in dignity"), and informs that the households have a longstanding feud ("ancient grudge") that has once again erupted into violence ("break to new mutiny").
The second line of the first quatrain tells the audience that the play is set "in fair Verona." Shakespeare set thirteen of his thirty-eight plays either fully or partly in Italy.
Italy was considered an exotic location where most of the people in Shakespeare's audience had never been, except in their imaginations. The Elizabethans' perception of Italians was that they were clever, sometimes devious, sophisticated, and extremely passionate in love and war, which might explain why Shakespeare set six of his love stories in Italy.
The second quatrain identifies the "star-crossed lovers" as the central characters in the play. They fall in love ("take their life," meaning they start their love life), they're going to suffer serious problems ("misadventur'd piteous overthrows") because of their love for one another, and that they're going to die because of their parent's feud ("with their death, bury their parents' strife").
The third quatrain identifies the overall action of the play (the plot), which will focus on the star-cross'd lovers' "death-mark'd love," which they try to maintain in the midst of their parent's feud ("the continuance of their parents’ rage").
The Chorus informs the audience that the feud—and the play—will end only when the two lovers have died for their love ("Which, but their children's end, naught could remove").
In the couplet at the end of the sonnet, the Chorus tells the audience to sit back (those who paid extra for a seat) or stand quietly in front of the stage, try not to be too rowdy, and enjoy the play.