An Overview - gst in india

• Individuals registered under the Pre-GST law (i.e., Excise, VAT, Service Tax etc.)
• Businesses with turnover above the threshold limit of Rs. 40 Lakhs. Upto 40 lakhs
• Voluntary registration
• Casual taxable person / Non-Resident taxable person
• Agents of a supplier & Input service distributor
• Those paying tax under the reverse charge mechanism
• Person who supplies via e-commerce aggregator
• Every e-commerce aggregator
• Person supplying online information and database access or retrieval services from a place outside India to a person in India, other than a registered taxable person

Small businesses having an annual turnover less than Rs. 1.5 crore can opt for Composition scheme. Composition dealers will pay nominal tax rates based on the type of business:

• Composition dealers are required to file only one quarterly return (instead of three monthly returns filed by normal taxpayers).
• They cannot issue taxable invoices, i.e., collect tax from customers and are required to pay the tax out of their own pocket.
• Businesses that have opted for Composition Scheme cannot claim any input tax credit. Composition scheme is not applicable to Service providers, Inter-state sellers, E-commerce sellers
  Supplier of non-taxable goods
  Manufacturer of Notified Goods

ISD means Input Service Distributor. It is like a head office that receives the tax invoices of input services and then further distributes the credit of tax paid by it to its units proportionately.

Yes the person can voulantarily can cancel the registration on wish.
Even proper office, on default of tax by taxable assessee will cancel the GST registration by giving notice.