GST registration is required for all existing taxpayers registered under central excise, service tax, VAT, entry tax, luxury tax or entertainment tax. The enrollment schedule varies by state, with dates ranging from November 2016 to January 2017. To register, taxpayers submit documents including PAN, business details, authorized signatories and bank details online at the GST portal. Upon approval, an Application Reference Number is provided and the registration certificate is issued within 3 days.