A metaphor is a figure of speech that makes an implicit, implied, or hidden comparison between two things that are unrelated, but which share some common characteristics
Metaphors are used to dramatize thoughts to emphasize and elevate the expression to a higher intensity. Recorded from the late 15th century, the word comes via French and Latin from Greek metaphora, from metapherein ‘to transfer’
Metaphors have comparison which is indirect. For instance, the sentence, "Riya is like a tigress" is a simile and the sentence "Riya is a tigress" is a metaphor. While both the sentences mean the same, we can easily understand that "Riya" is compared to a tigress in a more prominent and direct tone in the first sentence. In the second sentence, it looks as if the speaker is saying that Riya is a tigress rather than she looks or behaves like one.
1. The calm lake was a mirror- In the real sense, the lake cannot be a mirror. However, it can have the qualities of a mirror. It can stay still and can reflect things. Hence, the sentence means that the calm lake was able to reflect things very clearly.
The reflection of the tree seen on the lake is as good as the ones seen on mirrors 
2. Chaos is a friend of mine- The literal meaning claims that 'chaos is a friend of the speaker'. The metaphorical meaning is that 'chaos has been a part of the speaker's life for a long time'.
3The sun is a golden ball - The sentence doesn't mean that sun is ball made of gold or that you could run around and play with it. It actually means that 'the sun is in the colour of gold (or fire) and is in the shape of a ball.
Metaphors used in the poem "The Tale of Custard the dragon":
  • Mouth like a fireplace, chimney for a nose - The poet compares the dragon breathing fire and the smoke being let out as a chimney emitting smoke.