The document provides guidance on writing formal business letters in English. It discusses the standard structure and sections of a business letter, including the salutation, introduction, body, closing, and signature. It also lists common purposes of business letters such as providing information, apologizing, or responding to inquiries. Sample letters are given as examples for writing letters of inquiry, quotation requests, and replies. Key points about focusing on important details, acknowledging previous correspondence, stating actions, and inviting further questions are presented for structuring reply letters.