Salut ! Je te donne quelques idées pour rédiger ta lettre : 

a) When John Winterhayes left England, he was probably sad and unhappy. He was probably angry against the magistrate.
b) The journey took 3 months, so it was very difficult to survive. John didn't have a lot of food. 
c) The weather was hot, very hot at the day, but at night, it was cold. John didn't have a lots of clothes, only an old t-shirt and an old trouser. The food wasn't good, in fact, there wasn't a lots of food. John had to share the food with others prisoners.
d) During the day, John probably felt unhappy because he was far from his family, his friend, his house. He was probably sick because of the bad food and the weather.
e) When John arrived to Australia, he was maybe a little happy, because the journey was finish. He was probably worried because he didn't know what he will do at the prison. 

J'espère t'avoir aidé :)