The document discusses various types of letters such as formal letters, informal letters, and cover letters. It provides guidelines on how to write different types of letters properly, including the format and structure. Key points covered include introducing yourself in the first paragraph, including details in the second paragraph, and concluding in the third paragraph for formal letters. For informal letters, a casual tone is used without a strict format. Cover letters should complement resumes and explain why the applicant is suitable for the position.