Life’s but a walking shadow; a poor player, That struts and frets his hour upon the stage, And then is heard no more: it is a tale Told by an idiot, full of sound and fury, Signifying nothing.
It takes place in the beginning of the fifth scene of Act 5, during the time when the Scottish troops, led by Malcolm and Macduff, are approaching Macbeth's castle to besiege it.
Macbeth, the play's protagonist, is confident that he can withstand any siege from Malcolm's forces.
[1] Shortly afterwards, he is told of the apparent movement of Birnam Wood towards Dunsinane Castle (as the witches had prophesied to him), which is actually Malcolm's forces having disguised themselves with tree branches so as to hide their numbers as they approach the castle.
This sets the scene for the final events of the play and Macbeth's death at the hands of Macduff.