Metaphor compares without using the words ‘like’ and ‘as’ that we find in most similes.
Do not confuse symbolism with metaphor.
In metaphor the comparisons may be shockingly different, surprising, often pleasant, and revealing. A good metaphor is original and fresh. It does not have to explain itself.
Avoid cliché and overused comparisons.
Some examples
“My thoughts are stars I cannot fathom into constellations” – The Fault in Our Stars by John Green.
“And how my soul was as a lampless sea,” – “Epipsychidion” by Percy Bysshe Shelley
“Dying is a wild night and a new road” – written by poet Emily Dickinson in an a letter.
“Life: a lighted window And a closed door.” – “I Pass a Lighted Window” by Clement Wood
Write This
Write a scene or a poem to include at least one metaphor. Make sure the metaphor adds to the story without intruding. The metaphor must make sense inside the story and the POV, and should not be alien to the story or the POV. You may use more than one metaphor, if you dare.