The document discusses the key components of a business letter and an informal letter. It notes that a business letter contains specific structured elements like the writer's address, date, recipient's address, salutation, message body, closing, and signature. Optional fields may include the writer's initials, enclosures, and carbon copy recipients. An informal letter is less structured and can be written between friends or relatives about any topic, typically including a salutation, message, closing, and signature with an optional postscript.