A simile is when a writer compares one thing to another by using the word "like" or "as." You can see an example of a simile when Polyphemus the cyclopes first grabs two of Odysseus's men and kills and eats them. The narrator says that the cyclopes
gripped up two of my men at once and dashed them down upon the ground as though they had been puppies
By comparing them to puppies, the narrator is showing how little they were compared to the cycolpes. He then goes on to say that the cyclopes ate them as if he were a lion. That's a simile too. He is comparing the cyclopes to a lion to show how vicious and ravenous he is.