There is a stage direction just before the prologue begins, it reads "Enter Chorus." The job of the chorus was not to act but to go onto the stage and read out the prologue. The chorus wasn't an actual character in the play, just as the newsreader is not a character in the film version. The job of the chorus (and the prologue) is to inform the audience of the main storyline of the play, because the play is a tragedy not a mystery so it doesn't matter if the audience know what happens anyhow. The prologue had to stand out and gain the audiences attention because when the play was originally acted out there were no special effects or computer graphics. So when deaths or fights occured in a play it was difficult to make them look realistic without actually hurting or killing the person. If the audience is told what is going to happen, they will be able to visualise it for themselves.
When people see a play for the first time they interpret it in their own way, which is fine but can cause a misunderstanding of what the play actually means. So having the prologue before the play helps people understand from the beginning and so making the play more enjoyable.
The title states that the play is a "tragedy" and the prologue helps to emphasise this. The first section of the prologue sets out the scenario. The first line of the prologue reads "Two households, both alike in dignity." This line informs you about whom the characters in the play are and how many. In this play there are two households, this is not just mum, dad and two kids this also includes the more than the immediate family as well such as aunties, grandparents and even servants. This line tells us that the two households are both alike in dignity. This means both families are eminent and have stature. The fact that they are both alike could mean they are competitive, (remember the saying opposites attract, well these people are not opposites so the rule must be used in reverse, so would this perhaps make them repel? We"ll see.