Lady Macbeth shows her ambition for her husband to become king, but she's worried about whether he has what it takes to do what has to be done in order for this to happen. She says Macbeth is ambitious, but he doesn't have the cold-blooded desire to do whatever is necessary for him to become king. She says his nature is "too full of the milk of human kindness. . ." to committ murder. Lady Macbeth can't wait for him to come home so she can convince him that he must do any and everything to become king. She remarks that even fate and the supernatural forces want him to become king.

Enotes has wonderful side-by-side texts of many Shakespeare plays. They show the original text and a modern translation. Below is the modern translation for the passage you did not understand. What Lady Macbeth is saying is a "prayer" of sorts, but not to any Christian god. She is asking the spirits to remove any womanly feelings from her and make her cruel enough to do anything necessary--including murder--to help her husband become king.

The raven himself is hoarse
With croaking about the fatal entrance of Duncan
Under my castle walls. Come, you spirits
That hear mortal thoughts, take away my womanhood;
And fill me, from my head to my toes, full
Of most terrible cruelty! Make my blood thick,
Stop up the ways remorse can get into and leave my body,
That no feelings of guilt
Keep me from what I intend to do, or put guilt between
The consequences and the deed! Come to my woman's breasts,
And make my milk poisonous, you murdering ministers,
Wherever in your blind shadows
You wait on human mischief! Come, thick night,
And rot in the most gloomy smoke of hell so
That my sharp knife doesn’t see the wound it makes
Or that heaven peeps through the blanket of the dark
To cry, "Stop, stop!"

To see the entire modern translation, click the link below: