Act 1, scene 5 of Shakespeare's Macbeth opens with the first appearance of Lady Macbeth. She enters the scene reading a letter from Macbeth telling her about his encounter with the witches and their prophecies to him.
Within just a few lines, Lady Macbeth indicates that she intends to manipulate Macbeth into making that prophecy come true.
LADY MACBETH. Hie thee hither,
That I may pour my spirits in thine ear
And chastise with the valor of my tongue
All that impedes thee from the golden round.
When Macbeth appears in the scene, he tells Lady Macbeth that King Duncan is coming to stay at their castle, and Lady Macbeth decides that they should murder him.
MACBETH. My dearest love,
Duncan comes here tonight.
LADY MACBETH. And when goes hence?
MACBETH. Tomorrow, as he purposes.
LADY MACBETH. O, never
Shall sun that morrow see!
Lady Macbeth notices some hesitation from Macbeth about killing Duncan. She immediately takes charge of the situation and starts telling Macbeth how to behave towards Duncan when he arrives and says one of her most famous lines:
Look like the innocent flower,
But be the serpent under't.
Lady Macbeth doesn't trust Macbeth to do what she wants him to do, so she tells him, twice, that she's going to take charge of the situation herself.
LADY MACBETH. [A]nd you shall put
This night's great business into my dispatch.
Leave all the rest to me.
After Duncan arrives at Macbeth's castle, Macbeth has serious second thoughts about killing him, and he tells Lady Macbeth, "We will proceed no further in this business" (act 1, scene 7, line 34).
This is not what Lady Macbeth wants to hear. In her next speech, she berates Macbeth for changing his mind, accuses him of betraying her, says that he doesn't love her, calls him an indecisive coward, and says that he wants everything handed to him without doing anything to deserve it. Macbeth protests:
I dare do all that may become a man;
Who dares do more is none.
He means that he's done everything honorable to advance himself and that to do otherwise would be dishonorable.
Lady Macbeth takes his words literally. She calls him a "beast" who's broken his word to her, and she attacks his manhood, saying that a real man would do whatever is necessary to become king.
LADY MACBETH. When you durst do it, then you were a man;
And, to be more than what you were, you would
Be so much more the man.
She further emasculates and denigrates Macbeth by saying that she would kill her own baby rather than break a promise to Macbeth like the one that he made to her.
By the end of the scene, Lady Macbeth has convinced Macbeth to kill Duncan—or she's simply browbeaten him into submission—and Macbeth ends the scene by saying to Lady Macbeth something that she might say to him.
MACBETH. I am settled, and bend up
Each corporal agent to this terrible feat.
Away, and mock the time with fairest show:
False face must hide what the false heart doth know.