A metaphor is a word or phrase that is used to describe a person or object and in so doing makes an understood comparison; unfortunately, this 'understood' comparison is not always easy to understand. For example, 'Her sunny face was a pleasing sight'. Her face couldn't literally (in real) be sunny. By comparing it with the sun, we understand that she was a pleasant person. Technically speaking, metaphors are figures of speech.
You may think that metaphors are not important to learn or understand. However, in everyday life metaphors are used extensively and so it's handy to familiarise yourself with them. You could always make up your own metaphors too and see if they catch on!
Do this 11-plus English quiz and see if you can find the meaning of the metaphors.