Similes and metaphors make comparisons between items or things that are not similar, though a simile will always contain the following words: like, as, than, or resembles. If you do not have the words: like, as, than, or resembles, then you probably do not have a simile, it is most likely a metaphor.
Simile: Her face is as red as a tomato. Because the word "as" is present, it is a simile.
Metaphor: Her face is a tomato.