An idiom is a phrase which has a different meaning from the meaning of its components. The words which are used give some clues, but usually the meaning is totally different, this is the reason why idioms are considered so tricky for students who are not native speakers.
NOW LET'S PRACTICE!!!
Find the meaning:
"He's like a cat amoung the pigeons"
"To jack up the prices"
"Full of beans"
"I ' ll be a monkey' s uncle"
"To chip in"
"To cook the books"
"To blow the a raspberry"
You must take into account that there is not an easy way to learn idioms.