It is divided into three quatrains and one couplet. The first quatrain introduces the main theme or metaphor. The second quatrain extends the theme or metaphor. The third quatrain gives the poem an unexpected twist, called peripeteia. The couplet summarizes the poem; it gives the poem a concluding image (http://www.dummies.com/how-to/content/writing-a-sonnet.html).
One of Shakespeare's most popular sonnets is Sonnet 18:
Shall I compare thee to a summer's day?
Thou art more lovely and more temperate.
Rough winds do shake the darling buds of May,
And summer's lease hath all too short a date.
Sometime too hot the eye of heaven shines
And often is his gold complexion dimmed;
And every fair from fair sometime declines,
By chance or nature's changing course, untrimmed.
But they eternal summer shall not fade,
Nor lose possession of that fair thou owest,
Nor shall death brag thou wanderest in his shade,
When in eternal lines to time thou growest.
So long as men can breathe or eyes can see,
So long lives this, and this gives life to thee.
Here is a Shakespearean sonnet I wrote in 2006 about a bridge that Rob and I used to visit in St. Mary's, Ontario, called As I Stand on the Old Train Bridge:
O'er the river Thames the red sun disappears
As I stand on the old train bridge looking down.
I can almost hear the trains of yesteryear
Winding their weary way through the old stone town.
The river carves a path through the fertile ground.
Next to the running water lies a lush plain.
The grass is so green and the trees do abound
Where Jersey cows once grazed beneath passing trains.
Two ducks take a long drink after the soft rain.
As they hide behind a swaying poplar tree.
In the distance grows a field of golden grain
As far away as the naked eye can see.
As I stand on the old train bridge, silence speaks:
And a hush falls over the meandering creak.