A metaphor is a figure of speech that is used to compare two people, animal, places or things, comprising of an implicit contrast, wherein a word or sentence is compared to another. For example, "the snow is a white blanket”, “all the world's a stage", “the moon is a white balloon”, “her hope was a fragile seed.” They don’t mean exactly what the words say.
Metaphors use figurative language to connect one thing to another in order to highlight how they're alike. It suggests what something is like by relating it with something else with similar characteristics. Metaphors are so ordinary that you probably use heaps of them every day without ever realizing it. 'Life is a journey', after all.