It looks like it's asking you to write a pretend letter, based on the information from the first letter you read, using the prompts that state what needs to be included.
First, it's going to be a letter to John's mother, so you'd start the letter with something like "Hello, mother," or "Dearest mother"
Then, you write the body of the letter. Each of the things that need to be mentioned should have their own section. It doesn't necessarily need to be a paragraph each, but they all need to be separated. There are five parts (a,b,c,d,e on the worksheet), so there will be five sections.
The first section will be his feelings as he leaves England. Remember that he wasn't much older than you are right now, got arrested for stealing bread, and is being sent to the other end of the world. Is he scared? Is he angry that he got caught? Is he frustrated with the justice system?
The second section will state how long the journey took. That information is also in the first letter read, but make sure you add details. Was it boring or exciting? Were the sailors talkative or mean?
The third section is about the weather, food, and other problems. Was there a storm? Were the seas calm the whole time? Was the food any good, or did it taste like sawdust? Was he chained up in the ship, or was he allowed to roam free? Use your imagination to make his experience seem real.
The fourth section will be his feelings. Was he mad that he was so hungry? Was he happy about the sea breeze, or sad that he never got to feel it? Was he anxious to finally be on dry land? Put yourself in his shoes.
The fifth, and final, section is going to be about his arrival in Australia. How is it different from London? Does he think he'll like it here after he gets set free? Is he scared of what they're going to make him do for the seven years he's imprisoned?
To end your letter, I would suggest having him mention that he misses his mother, or how he's sorry that he screwed up and had to leave her. Have him say something about how much he loves his mother, and then it ends with "Love, John" or "Sincerely, John" or however you think he would sign his letter.
If you'd like, I can proofread your letter after you're finished writing it. Good luck!