What could you use a metaphor in?

You could use it in a story or a poem. For example:

Story:

Once upon a time there was a girl who hated her dad. He was a pig. He ate so much that he didn't properly do anything...to be continued.

The metaphor is "He was a pig." It is a metaphor because he wasn't literally a pig.

Poem:

I once had a dog. He hopped like a frog (note: that was a simile, not a metaphor). He ate till he was big and became a pig (the metaphor:Again he didn't magically become a pig; he just ate a lot.)