The document explains the Harmonised System of Nomenclature (HSN) codes and Service Accounting Codes (SAC) for the classification of goods and services for taxation purposes under the GST regime in India. It outlines the details required on tax invoices, bills of supply, and debit/credit notes, including the necessity of providing information such as the supplier and recipient's details, applicable rates, and HSN/SAC codes. The document also describes the procedures for issuing delivery challans and dealing with various taxation scenarios.