What is it?
Metaphor is a figure of speech that makes a direct comparison between two unlike things. A metaphor suggests that one thing is another thing, or is equal to another thing.
Why is it important?
Metaphors create vivid descriptions with few words, as the subject of the comparison takes on the qualities of the thing with which it is compared.
How do I do it?
Compare two dissimilar things without using the words "like," "as," "than," or "resembles." Either state the comparison outright, as in Example 1, or attribute the qualities of one thing to another thing so that the reader infers the comparison, as in Example 2.
"All the world's a stage,
And all the men and women merely players;"—William Shakespeare, As You Like It
Note: Shakespeare uses the theater as a metaphor for life. He extends the metaphor by writing that people are simply the actors upon this "stage" of life.
"Leaves got up in a coil and hissed,
Blindly struck at my knee and missed"—Robert Frost, "Bereft"
Note: Frost compares a windblown coil of leaves with a striking snake. Rather than using the word snake, he attributes snake-like qualities to the leaves to convey a certain image and mood to the reader.