The document discusses different types of letters including formal letters, informal letters, business letters, and demi-official letters. It provides characteristics and formatting guidelines for each type. For formal letters, it indicates they are written to someone unknown and discuss work, business or official topics. Examples of formal letters given include letters of enquiry, application, complaint, and regret. Guidelines are provided for the layout and content of each paragraph in formal and informal letters. Business letters are described as a convenient means of communication and record keeping, with examples like official, demi-official, and internal letters. Finally, demi-official letters are defined as a type of business letter written to specify someone exactly, like a vice chancellor.