Question

What is hyperbole?how it is used in poetry ?

Answer 1

Hyperbole is used to give extra- effects by the means of exaggerating.
To make it clear for you, have a look at some of the examples-
My grandmother is as old as the hills!
Your suitcase weighs a ton!
She is as heavy as an elephant!
I am as tall as a tree!

Do you see? All these are actually not possible. This is called exaggeration. 
Coming to your question- How is it used in poetry?
Well, Hyperbole is used in a poetry to make it come out very extra-ordinary with great effects but might not be possible in reality.

I'll give you an example of the poem “As I Walked One Evening”,

I’ll love you, dear, I’ll love you
Till China and Africa meet,
And the river jumps over the mountain
And the salmon sing in the street,
I’ll love you till the ocean
Is folded and hung up to dry.

How on earth will china and Africa meet? and have you ever seen a river jumping over mountains? My word! How can an ocean be folded and hung up to dry?!?!
Being funny it still beautifies the poem.!!

Hope this helps you..!! :)