Theory:

     “Djinn of All Deserts,” said the Horse, “is it right for anyone to be idle?”

 

     “Certainly not,” said the Djinn.

 

     “Well,” said the Horse, “there’s a thing in the middle of your Desert with a long neck and long legs, and he hasn’t done a stroke of work since Monday morning. He won’t trot.”

 

     “Whew!” said the Djinn whistling, “that’s my Camel. What does he say about it?”

 

     “He says ‘Humph!’, and he won’t plough,” said the Ox.

 

     “Very good,” said the Djinn. “I’ll humph him if you will kindly wait a minute.”

Explanation:
  
As soon as the Djinn appeared, the horse asked the Djinn, whether it was right for anyone to be idle.
 
The Djinn said it was definitely not right for anyone to sit idle.
 
The horse asked him about the camel; he said there was a thing in the middle of the desert and that he had a long neck and long legs. The horse complained that the thing had not done any work since Monday morning; nor did he move.
 
The Djinn immediately realized it was the camel that the horse was talking about. The Djinn asked the horse what the camel said when they asked.
 
The ox replied that the camel said "Humph" and that we wouldn't plough.
 
The Djinn asked the animals to wait for a minute and said he would humph the camel. The Djinn meant that he would deal with him in the right manner and set him right appropriately.
 
Meanings of difficult words:
  
Words
Meanings
stroke of workno work, any work at all
whewexclamation used to express surprise, relief, or a feeling of being very hot or tired.
humphdeal with him appropriately (here)
Reference:
National Council of Educational Research and Training (2008). How the camel got his hump - Rudyard Kipling (abridged) (pp. 01-06). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.