The first link below gives a modern interpretation of the entire scene. You will find links on the left side of that page for a modern translation of the entire play.
In this speech, Hamlet is sad and angry about the death of his father and his mother's hasty marriage to Claudius. He is so distraught and frustrated that he compares the world to a decaying, unweeded garden. The world is now useless in his eyes, being weary, stale, flat and yielding no fruit or no profit.
Hamlet goes on to complain that his father was magnificent and Claudius is a "beast." Hamlet is upset that his mother married Claudius so quickly after the king's death.
Ere yet the salt of most unrighteous tears
Had left the flushing in her galled eyes,
She married. O, most wicked speed, to post,
With such dexterity to incestuous sheets! (I.ii.157-160).
A modern translation of these lines would be as follows.
Even before the salt of her dishonest tears
Had left her crying, swollen eyes,
She married. This is awfully quick to go,
With such aggressiveness to sleep with her brother-in-law.
Hamlet says that Gertrude married Claudius so quickly after the king's death that it shows a lack of an appropriate grieving period and it reflects badly on Gertrude's character, having gone to bed with Claudius so soon. The reference to incest is because Claudius is/was her brother-in-law.