Business letters are the primary means of formal communication between organizations. They have specific components, including a letterhead, salutation, body, complimentary close, and signature. The body contains an introduction, main discussion, and conclusion. Business letters are used for various purposes like placing or acknowledging orders, filing complaints, sending invoices, and more. Common types include sales, order, complaint, adjustment, and follow-up letters. Proper structure and components ensure business letters are clear, professional, and achieve their intended purpose.