What happens
Lady Capulet sends for Juliet. She wants to talk about marriage. The Nurse, fond and voluble, launches into a long memory of Juliet as a baby — earthquake, weaning, an off-colour joke from her late husband — that Lady Capulet politely tries to cut short. Eventually Lady Capulet asks: how do you feel about getting married? Specifically, to Paris? Juliet, reserved, says she'll "look to like, if looking liking move" — she'll see if she can make herself fond of him. The conversation ends with the household summoned to the Capulet feast that evening.
Why it matters
This is Juliet's first scene. Shakespeare introduces her by way of two older women trying to define her — her mother coolly, the Nurse warmly — and Juliet listens. She speaks last and least. "It is an honour that I dream not of" is one of those lines that means three things: a polite formula, a literal truth (she hasn't thought about marriage), and a piece of wit (it's an honour she doesn't even dream of). Already, before she's met Romeo, Juliet is the play's most careful speaker.
The Nurse's speech is played for laughs but is doing real work. It tells you Juliet is exactly thirteen years and ten-or-so months old. It tells you the Nurse lost a daughter named Susan around the time Juliet was weaned. It tells you the Nurse has been Juliet's de facto mother since infancy — closer to her body, her habits, her temper than Lady Capulet has ever been. By Act 3 Scene 5, when the Nurse abandons her, the betrayal is the size of this scene.
Lady Capulet's framing of Paris — "the valiant Paris seeks you for his love," described as a fine book, a bound volume — is also a piece of the play's argument about love. She's selling her daughter on a man via metaphor, telling Juliet to "read o'er the volume of young Paris's face." Juliet hears it, agrees to look. Tonight she will look — at someone else.