Supply as the taxable event under GST governs levy, exemptions, reverse charge, and composition scheme eligibility. Article 246A establishes GST legislative competence and identifies supply as the taxable event, with intra State supplies attracting CGST and SGST/UTGST and inter State supplies attracting IGST. The law defines composite and mixed supplies with distinct tax rules, provides for reverse charge on notified supplies and for electronic commerce operators to be made liable for tax on certain services. The Composition Scheme offers simplified rates subject to aggregate turnover thresholds and specified exclusions; composition taxpayers cannot collect tax or claim input tax credit. Governments may grant absolute or conditional exemptions.