This speech is surely one of the most quoted in Shakespeare. Life, in Macbeth's tortured view, is described through a series of metaphors, one quickly following another.
Life is a candle which, in the past, has "lighted fools the way to dusty death." Macbeth sees himself among this company, as he faces his own death, the result of his own foolish decisions. For him to say "Out, out, brief candle" suggests that he is ready to die.
Life is a "walking shadow" and a "poor player." It "struts and frets his hour upon the stage and then is heard no more." Macbeth refers to his own life; it is he who has strutted and fretted during the short time he wielded power in Scotland, a bad actor on the stage of his country's history and one who will not live in its collective memory.
Finally, life is "a tale told by an idiot." Again, Macbeth assesses life in terms of his own. His life has been full of "sound and fury," but it signifies nothing at all. He leaves behind him nothing of value.
Life is a candle, a shadow, an actor, one brief hour upon the stage, and an idiotic tale. Macbeth's bitterness and despair are communicated strongly through these metaphors.
Lines 21-30 in Act 5 Scene 5 of Shakespeare's Macbeth are spoken by the title character after the death of his wife, known to the audience as Lady Macbeth.
In this soliloquy, Macbeth uses metaphor to lament the uselessness of life. When Macbeth says "Tomorrow and tomorrow and tomorrow, creeps in this petty pace from day to day to the last syllable of recorded time" (lines 19-21) he personifies the future and compares it to a creature that moves very slowly. A creature that moves very slowly can be seen to lack purpose.
He then compares life to a candle "Out, out, brief candle." The image of a candle being snuffed out conveys the nothingness, the futility of life. Next, he compares life to a "walking shadow." When a person walks on a sunny day, their shadow moves with them, seeming to be a living thing, yet it lacks all substance. Macbeth compares life to that shadow, devoid of substance.
Life is then compared to a "poor player that struts and frets his hour upon the stage and then is heard no more." This comparison to an actor who is perhaps flamboyant, certainly animated, but then never heard from again signifies again the brevity of life.
The final metaphor compares life to a tale, but not just any tale. It is a "tale told by an idiot, full of sound and fury, signifying nothing." If life was simply compared to a tale, it would still have structure and meaning. But the fact that it is told by an idiot shows that it is again loud and showy, but with no depth, no substance, and no meaning. I've added the lines below for reference:
"Tomorrow, and tomorrow, and tomorrow,Creeps in this petty pace from day to dayTo the last syllable of recorded time,And all our yesterdays have lighted foolsThe way to dusty death. Out, out, brief candle!Life’s but a walking shadow, a poor playerThat struts and frets his hour upon the stageAnd then is heard no more. It is a taleTold by an idiot, full of sound and fury,Signifying nothing."