As in all dramas, the characters and the conflicts/problems are introduced to the audience in the first act, which contains the exposition and the initial action, and Act I of Shakespeare's Romeo and Juliet is no exception. Of course, the Prologue provides the Elizabethan audience a summary of what it to come in the play, despite the fact that audiences were probably familiar with the story of Romeo and Juliet since it was already known and very popular when Shakespeare came to write the play around 1594.
In Act I the antipathy of the two households, Capulet and Montague, is introduced by the exchange of insults among servants from both families. To underscore the acrimony of these families, the old Lords Capulet and Montague come out to the street and insult each other as well. As a result of the renewing of the feud, the Prince of Verona issues an ultimatum to anyone who breaks the peace. Then, Romeo is presented as the melancholic victim of unrequited love. For, Rosalind has rejected him and gone to the convent, leaving Romeo to wallow in self-pity. His good friend Benvolio suggests that
One pain is lessened by another's anguish...
One deperate grief cures with another's languish. (1.2.)
Thus, he encourages Romeo to mask himself and join him and Mercutio as they sneak into the Capulet's party for their daughter Juliet. This fateful action of going is the catalyst for Romeo's being starstruck by the beautiful Juliet and is, thus, pivotal to all the following acts of the play