What is the difference between ( I will ) and ( I shall ) ? What is the difference between ( I will ) and ( I shall ) ? Kindly give me the meaning in simple language ( with example ) if you please ..

I have an assignment and i need someone to correct my writing This story is for kids , so don't be surprised :) [ The Body Changeling ] One Day , there was a fat boy called " John " playing in the garden with his ball , he was very kind boy , but his only problem was eating too much Fast Food and Candies , this problem was the reason why his friends underestimate him all the time . While John was playing , his friends saw him , and started laughing at his corpulence , but one of them called " Tom " ( the closest friend of John ) was always sad for his situation , so he decided to talk to him , Tom said : Hey John , what's your problem Dude ? How long do you want to stay this way ? John said ( with sad expression ) : Huh! I don't know ! Tom said ( with anger expression ) : I will let you go now , but think about it , and you will not regret it (then he went away ) . After That , John started thinking , he stares at the sky , and said : He's right ! Thus he decided to workout Daily , follow a hard diet , and get away from his friends for a period of time . After 6 months , John came back with a very nice body , he went to the same garden which he played in it and saw his friends again , they look at him but they didn't know who he is ! but when he started talking to them , they knew him immediately and were really shocked , then they gathered around him and congratulated him , and forgot the old John whom knows , then his close friend Tom finally said ( with a big huge smile on his face ) : Great Job Bro! ( Sorry for the long story )