Macbeth has sent Lady Macbeth a letter. In Act 1, Scene 5, she reads the letter out loud to herself. The letter tells her about how Macbeth met with the witches and what they said to him about one day becoming the Thane of Cawdor and eventually the King. She is quite moved by the news but doubts that her husband has what it takes to act decisively, boldly, and viscously. She says:
Glamis thou art, and Cawdor, and shalt be
What thou art promised. Yet do I fear thy nature;
It is too full o’ the milk of human kindness
To catch the nearest way. Thou wouldst be great;
Art not without ambition, but without
The illness should attend it. What thou wouldst highly,
That wouldst thou holily; wouldst not play false,
And yet wouldst wrongly win. Thou'ldst have, great Glamis,
That which cries, “Thus thou must do, if thou have it;
And that which rather thou dost fear to do
Than wishest should be undone.” 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,
Which fate and metaphysical aid doth seem
To have thee crown'd withal.
Very knotty use of the English language there in bold face, for sure; no doubt it was a quote more familiar to people in Shakespeare's time than in ours. But what she is saying to her absent, but shortly-to-arrive husband, is this: "You need someone to tell you what have to do, and you shouldn't be afraid to do something to the point of wishing it never happened." Then she says, as befitting the quote: "Come on home, and I'll make sure to convince you to get what you were promised and what you so richly deserve."
Ah, what a woman!
Lady Macbeth is saying "You want to have, my husband Macbeth..."
Remember, Macbeth is the Thane of Glamis already. Lady Macbeth believes the three witches' prophesy 100% and knows he has also the been given the title Thane of Cawdor and will thus soon be the King.
"Thou'ldst have" means "You want to have." Then she goes on to suggest how to get what she knows he wants (or at least what she will convince him that he wants).
In her first soliloquy, Lady Macbeth tells us her opinions of Macbeth, and before she delivers this line she states that Macbeth does not want to "play false" in obtaining the crown, but then she delivers the line that you have here, and what it means is this:
Consequently, this is what you have to do, if you want to be king.