To write an informal letter as a teenager, first of all you have to write sender's address i.e., your own address so that the receiver knows where to send the response. Add date on which you are writing the letter and then add salutation such as "dear cousin". After all this, you write the body of the letter containing all the details such as asking the person "how are you", giving information about your well being and the main topic of the letter. At last close the letter by writing "yours lovingly", "with love", etc.
"Informal letter is a personal letter that is written to let your friends or family know about what is going on in your life and to convey your regards."
While writing this letter as a immigrant you have to keep in mind the scenario of 1900's in United States. You must include your personal experiences of living as an immigrant during the past one year, the opportunities you had, the issues you faced during your stay. You can write about your impressions of the United States.
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