This document provides guidelines for writing emails and letters both informally and formally. For informal emails, it recommends starting with a greeting like "Hi" and ending with something casual like "Talk to you soon." Formal emails should use the same greetings and closings as formal letters, which typically start with "Dear Mr./Ms. Last Name" and end with "Sincerely" followed by the full name. The document outlines appropriate language and structure for both informal letters to friends and formal letters such as for business.