The Chorus (kind of like a narrator) appears on stage and gives us the low-down on the play we're about to watch (or read).
The setting is "fair Verona," a town in Italy where two rival upper-crust families (the Capulets and the Montagues) have been feuding for as long as anyone can remember.
We're also told how the children of these two families (that would be Romeo Montague and Juliet Capulet) will fall in love, but the story's not going to be a happy one. Before the play is over, our infamous "star-crossed lovers [will] take their life" (commit suicide), which will put an end to their parents' feud.
Finally, the Chorus invites us to sit back and relax while we enjoy the "two-hours' traffic of [the] stage," which is sixteenth-century theater speak for "the two hours it's going to take for the play to be performed."
Brain Snack: In director Baz Luhrmann's 1996 film adaptation of the play (Romeo + Juliet), the Chorus is replaced by a T.V. anchorwoman who delivers the lines as an evening news story.