This is something that Macbeth says in response to hearing that Malcolm, King Duncan's son will be the heir to the throne. The entire quote reads;
Stars hide your fires; Let not light see my black and deep desires: The eye wink at the hand: yet let that be. Which the eye fears, when it is done to see.
What Macbeth is asking for here is impossible. He would like the stars to go out (Stars hide your fears) so that no one can see what he wants, not even himself (Let not light see my black and deep desires). He asks that his own eye wink, or go blind, so that his eye cannot see what it is that his hand wishes or desires to do (The eye wink at the hand;). The final part of the quote is saying that he wants to just wants to let it be even though he knows that his own eye will be afraid to look at what it is that he's done (yet let that be. Which the eye fears, when it is done to see).
Macbeth has just discovered that King Duncan named his son Malcolm as his successor, which creates another obstacle for Macbeth to overcome. He has decided to do what he needs to in order to become King, but knows that he may regret such actions. This statement illustrates those conflicted feelings: Let my eye not see what my hand does, yet let me be successful.
Macbeth wants to let his own eyes be blinded to what his hands will do against Duncan because he is ashamed to see what the outcome will be: regicide through Duncan's murder.