What do you know about letters? What is the first thing you think of when you think of a letter? Is a letter personal or impersonal? Why would
someone write a letter?

a letter is a written form of communication.

the first thing I think when i think of a letter is a stamp, envelope and something to read.

a letter is categorized into personal and impersonal(which is formal)

reasons for writing a letter;

basiclly a letter is a form of communication that can be elaborate,funny,open as wished when sent to friends and families but can be formal,authorized and improvised when it's impersonal and is sent to a titled person.